UK grid frequency is currently 49.952Hz ( you can check yourself - http://gridwatch.templar.co.uk/)
The National Grid is (IIRC) legally required to be within 49.5 and 50.5hz. I personally wouldn't rely on the grid being that accurate.
Shouldn't they have it on a UPS generating a pure sinewave at precisely 50Hz if it's THAT important that their supply be completely, perfectly accurate? I'd hate to know what that lot would be saying if somebody on the same circuit started arc welding or similar...
Biting the hand that feeds IT
