I'm applying for ESRC PhD funding but am a bit worried about proving the 3 years UK residency requirement - I'm a UK citizen and by the time of the award starting will have been resident in the UK for 2 years, but before that I was working abroad for a year although for tax purposes was employed by the London office of my company and was officially considered a UK resident. Does anyone know what kind of proof is needed to show that this time was a 'temporary absence'?

Surely as a UK citizen you aren't required to prove residency?

Yes you are - they say explicitly that UK citizenship is not sufficient, you are required to prove your physical presence in the UK.

the research councils, worried about having to pay some money to other EU nationals, introduced this requirement to avoid other EU nationals en masse being able to claim funding. at the same time they created bureaucratic difficulties because OF COURSE they did not mean to make brits who went abroad for a while uneligible, so they had to include lots of complicated exceptions. are you paying "home" fees (rather than "home/EU","overseas")? then you should be eligible. the intention of the rulings is clearly that you should be eligible. the wording is less clear. you need to talk to the registrar at your uni. explain your situation in detail (from when to when you were in Britain, when you were abroad, for how long, with what intentions, do you have family in Britain, did they stay when you left, is the rest of your family also British & in Britain, etc). there is no general way to find out - just your particular case which you need to make.

If you were only working abroad for a fixed term, as part of a job/career based in the UK it won't be a problem at all.