How about a fairly basic phone by Nokia (model C2-01) at Three on PAYG at £29.99 (+ a £15 top-up)... That'd be on their 321 PAYG tariff - 3p per minute, 2p per text, 1p/MB of data (but unlikely you'd use much/any data with it).
A top-up does not expire (most other networks expect you to top up 5/ 7.50/ 10 per month) so with £15 you have 500 minutes OR 750 texts OR data OR (clearly and most likely) a mix of texts and calls. If you start making more than 500 minutes of calls a month, then getting a SIM only deal (and paying a monthly fee) would become more economic. That phone has a 3 Mp camera (not the highest resolution but should be enough or snaps) and it has all the numbers on buttons so not touch screen.
It would need a signal from Three, so depends where you live and where you'd spend time, so if you're in Scotland, N Ireland, or Wales, it may not be the best choice (just based on random observations about {lack of} Three coverage in the country in some parts.
Obviously if you have been using a work mobile, you might already have some model in mind, and there would be a wide range of phones from £50 to £500 depending on what you were used to using and what your budget would be.
Asda PAYG is another option (they do a range of phones which include some I consider a bit overpriced at present - eg Sony Xperia Tipo is £97 at Asda but I paid £50-60 from O2 and T-Mobile - will explain more about why I have 2x Sony Tipo another time). Asda uses the Vodafone network which has pretty reliable coverage across the UK, and the PAYG rates are fairly good (Which? mag winners in recent years), but quite a lot more expensive than the Three PAYG 321 tariff, if that would work OK for your locality.
Probably an idea to put some limits on what you would be willing to pay for a phone, and whether you know what networks work well in your area.