As others have said, think a Ryzen system would be ideal. I have a Ryzen 2400 (4 cores/8 threads) which powers my HTPC system and blazes through anything I throw at it (it's also good for basic gaming though you said that's not important). As you can get W10 for cheap (above eBay link), strongly suggest getting an SSD and your budget should allow for it. If your GO work and image processing needs space, can you use an existing external HD or buy a large mechanical further down the line. SSDs do make a nice difference over mechanical. A DIY system from e.g. OcUK comes to:
Ryzen 5 3400G - £140
B450 motherboard - £100
Case - £50
500w PSU - £50
256GB/512GB SSD - £35/£60
8GB of 3000MHz RAM - £63
£438/£463 (used a thread on their forum for reference -
https://forums.overclockers.co.uk/threads/budget-build-second-pc-for-light-gaming-500.18868170/ )
However for a little more money, you could buy the suggested pre-built PC from Chillblast PCs which is hard to beat.
Edit - just seen the full specs of the suggested Chillblast PC, decent! It's got a slower processor that my suggestion but has double the RAM!! No brainer