Unless I'm very much mistaken then vinieco is not a 'fellow sparky' I'll apologise if I'm wrong.
I have a retail shop I run my sparkyness from and regulaly have DIYers in asking for 40/45/50 amp MCB's just like the 30 or 32amp version they bring in. Most of the time they have bought a 10.5KW shower from B&Q to replace their 7.5KW and then wonder why the MCB keeps blowing. The answer-uprate the MCB without a thought about the poor old 6mm cable in the wall. My answer is usually to ask them if they intended to install a heater in the wall and loft.......