PhilJ,
It is 250 total time at which the instructor's course can be commenced..
The information is to be found in LASORS; if you haven't got a copy, then get it. Costs about £10 from various avaition suppliers or you can download it and print it for free (aside from the cost of the paper, ink and download time).
Most people I have spoken to believe that it is best to do your training in the country in which you wish to work. Also be aware of any FAA conversion costs in the UK.
Cheers
Whirlygig