I have an old Wylex consumer unit, like this:
http://www.tlc-direct.co.uk/Products/WY804.html

I've bought an 9.5kW electric shower, but I've just discovered that
Wylex don't make 45A MCBs for these consumer units anymore, the highest
rated they produce is 40A. At 230v, 9.5kW draws 41.3A. Will I get away
with a 40A MCB or will it be forever tripping? (I have 10mm cable, by
the way, so 40A won't be a problem there).