Well, the nice man from British Gas came round and did a very neat job, and we are all 100A now. Cool.
Unfortunately there was another side effect of having everything re done that has added a lot to the cost! A new washing machine.
Turns out the old one had an earth leakage issue but was not tripping the old circuits (may have been one of the non RCD circuits), and so as soon as we put in RCBOs, we find it is duff.
All good fun.
P.S. the geek in me that passed A-level physics can't help feeling there should be something more fun and youtube worthy to do with a 100A power feed than just charge a car and run a tumble dryer at the same time. Shame.