The only chipset that currently supports Coffee lake is z370 and those motherboards are well beyond 50£
On your budget i'd suggest going with a Ryzen 5 1600.
There arent any motherboards in that price range available yet for the 8th gen cpus, currently only the more expensive Z370 motherboards are available for the new platform.
Only Z370 motherboards are compatible with this cpu. Their price starts from ~ $120.
For £50 you can't get a compatible motherboard at the moment.
Low cost coffee lake motherboards are scheduled to get released in next year.
read up on both chips. the older intel cpu wont run on the newer 370 chipset and the new coffee lake cpu need the newer mb they wont run on the older intel mb chipsets.