You cant keep opening another ISA every time you hit £50k, the admin would get too much.

I think that the word should be "could" and not "would". The advantage of ISA's is that you yourself have little to no administration. Limited possibly to re-investing dividends once or twice a year and adding details of new accounts to the list looked at by your loved ones in the event of your death.

I do agree with Gengulphus that there are many far more important things to think about than the FSCS. However there is also IMHO a difference between accounts with the likes of Selftrade, III et-al and the likes of the big banks, funds industry, or some traditional stockbrokers.

I am not unhappy with my Selftrade account, but will be looking for another provider by 2013. I was however quite happy to continue contributing to my traditional stockbrokers ISA long after it exceeded the FSCS limits. Then again they are a partnership and my funds are not just protected by the nominee structure but also by the fact that each partner is personally liable to the firms clients. (The law differs between plc's, llc's and old style partnerships).