You should contact a qualified Electrician - not ask on here. Please…
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Have booked someone in.
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It’s probably fine, as you are very unlikely ever to have all circuits at full capacity. That’s over 15KWatts. If you are using that much with todays prices, then you probably need to find a second job 
. Your Main Meter fuse is probably rated at either 80a or 100a. But an electrican will be able to check all that and test the RCD to ensure it is in spec.
FWIW That’s not right, as your garage is already limited to 6Amps from the MCB in your Lounge CU.
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Thanks, I’m hoping a “ramp test” will show the RCD is out of tripping tolerance.
The total load on your consumer unit is not the sum of the MCB ratings, this is the calculation you have performed. The load is the cumulative loads of the appliances connected which will hopefully be a lot less!
BTW the current rating, i.e. the load current which the ‘red encircled device’ is rated to pass is up to 63A, or 15kW. the RCD sensitivity is given by the number to the right 0.03A or 30mA.
This RCD figure indicates the maximum current (very small) that can pass from the live conductors to earth before it trips. You really should not increase the value of RCD tripping current. The RCD element of your 63A circuit breaker is a life safety device designed to minimize the risk of electrocution should a fault occur.
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The RCD will trip at 30mA. This is totally different to your main switch of 63A.
RCDs are set with an extremely low value to protect life.
“30 mA It is essential that the detection of the RCD is below the minimum anticipated current through the body and in fact the recommended tripping current for shock protection is a maximum of 30 mAand this is the current recommended in the Wiring Regulations.”
As you’ve advised, you have a competent electrician to test. Ensure that they are Part P Registered.
DG…
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An electrician won’t be able to find the problem device. He can check the circuits and perform a system test.
Can you run an extension lead from your fridge to an area covered by your other RCD. It looks like you have 2 RCDs so plug the fridge into one of the other areas. And it may take some time to show before it trips again.
I have been through all of this and ended up fitting RCBOs for every circuit. This means the individual circuits are tripped only as each MCB effectively has its own RCD.
RCBOs are expensive but will stop these nuisance scenarios in that you can see immediately which circuit the problem is on.
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Sparky couldn’t come today but by process of elimination it now looks like the upstairs lighting is causing the issue.
I flicked the MCB for the upstairs lighting off and it didn’t trip for 24hrs. Flicked it back on again and it tripped within the hour. No lights were on when it tripped.
I’m guessing you may have some LED lights upstairs, possibly some with transformers.
Is the lighting cabling within a roof-space and/or is a loft light on the same circuit? If so, it could be that some moisture is getting in to the junction boxes, caused as the temperature drops (akin to condensation). I’ve found spiders’ webs in these boxes, which then hold the moisture and short the circuit on an erratic basis.
Of course, it could be many other reasons but if you are DIY minded and can see some of the boxes (usually round), it might be worth a look.
UPDATE - Sparky has struggled to come around so I flicked the mains and disconnected the fused spur for the boiler and was faced with this:
Looks like the earth cable has a split in the green / yellow sleaving and “may” have been touching the screw hole / plastic casing for the socket.
I’ve re-sleeved it and (touches wood / fingers crossed) it hasn’t tripped for over 24-hours.
If this is the culprit (please let it be) surely it would be tripping all the time and not at random times through the day / night ?!?
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Earth touching the case shouldn’t cause it to trip. if it was a metal backing box it would be earthed anyway
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Swap your Hager type AC RCD for a Hager type A RCD
You might be looking for faults where there are none - just natural earth leakage from appliances.
The type A will deal with this much better than a type AC.
UPDATE TO THE UPDATE - Turns out the NEUTRAL wire of the Boiler also had a nick in it so have re-dressed that now.
Sparky reckons that the fix I did on the EARTH “accidentally resolved” the problem as that NEUTRAL was likely touching the NEUTRAL and causing the trip. When I re-fitted the spur cover I moved EARTH and NEUTRAL out the way so they were separated from each other.
It hasn’t tripped for x48 hours now so am hoping this fixes the problem. He did a full test on the entire housing circuit and couldn’t find any issues elsewhere.
Thanks for everyone’s advice. Finally I can plug all my NAIM kit in now as it’s been of for two weeks !!!
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It’s one of the eternal mysteries of running electrics that the sparkies and DIYers (who lay in cables only of course), try and dress the runs and conduits so very carefully but when it comes to back-boxes and pattresses where sockets & switches are involved, the cables are often forced in, often with brute force.
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…yep. And typically with about 2" of cable left to play with !!!
FYI, under ‘code’ now it’s my understanding that installations can ‘fail’ if the rubber donuts haven’t been inserted in to the cable feed/access holes used, noting many back-boxes have been sunk in using bonding plaster et al. OK – but the cables haven’t been stripped at this point but are stuffed in the box tight and bent to hell!!!
A good sparks always pushes a bit of cable back in to say a cavity, just in case.
Of course, this is the issue with all the mains wiring threads and trying to navigate 6 & 10mm cables in to tight spaces 
UPDATE - This has been fine for a week and now tripped twice this morning 
Interesting stuff on here, so to something less interesting 
;-
We moved house last year after a long renovation project. At the previous house we had a traditional fuse box and a separate fuse box and circuit for the HiFi fitted as an afterthought. If I’m honest, I’m not sure I could ever tell the difference… well no I couldn’t but the system never took out a fuse. So the issue of ‘what to do’ when having the new place rewired was quite high in my thinking. The sparks informed me that I had to have an RCD? box and that included any separate box I may want for the HiFi (all three sparks that I had estimate for the job had no idea why anyone would want to do the dedicated mains thing by the way). Taking into account my doubts about the effects at the other house, added to the new mains board I had to have’ I felt it pointless to go down that route again.
Added to that, I knew which room the HiFi would be in but not where in that room it would end up so, a compromise I reached was to have that one room on it own circuit but within the main board and to have several unswitched sockets in pairs of two wired in 4mmT&E(sparky wouldn’t do anything heavier). Therefore, the only other things on the ‘hi fi circuit’ are a TV and a couple of table lamps.
However, the system has tripped the circuit when I’ve changed things around, speaker cables, snaics etc. even though I have always done this with ALL components switched off and unplugged at the wall, which I do find a little odd.
oh no hope you figure it out