You may be confusing the terms and parts; the whole "box" is usually called a consumer unit (CU) and the RCD is that special switch at the right of the CU which will trip if it detects electricity going where it shouldn't. There is no reason to suspect that there is anything wrong with the CU or RCD. The 40amp miniture circuit breaker (MCB) is like an old fashioned fuse. As said it could be tired and a new 45 or 50A MCB is probably all you need.
I'd suggest getting an electrician to check the CU and fit another MCB. You do not show any other switches before the CU, so, if doing it yourself beware, unless there is a main isolator switch, parts of the CU will remain live even when it is switched off.
Edit see TTC has already made the point
Ahh, Yes I was a bit confused by all the different terms, so thanks for explaining that.
I will get in touch with an electrician and have it checked out and a new MCB fitted I am hoping that will fix the problem.