I asked this question earlier this year and I was told some do have UPS's but most do not. If an engineer was nearby and it was suitable to set up a generator he would do.
I was told this by various members of CF and NTL but this information could have changed over the months.
I have a UPS for all my PC's and I find them convenient simply because they protect from surges as well as blackouts, of which ive had a fair few since I got mine. The lights flicker and the UPS kicks in, and I feel all smug as my pc keeps running