Do you already have any chisels?
If yes: You don't need many chisels. 3 or 4 will be enough for most jobs. On your budget (£60?) I'd buy two good chisels. 1/4" and 3/4" perhaps.
Ashley isles are in that budget and excellent.
If no: I'd recommend buying a cheap set. I started with a set of
Vaunt chisels. Having a set of chisels that I was happy to use and abuse was a great starting point and I still use them a lot in spite of having a set of Ashley Isles for fine work. They will also teach you which size chisels you actually need. In your budget getting a cheap set would also allow for a cheap set of
diamond stones. Learning to sharpen is a key part to chisel work. A well sharpened cheap chisel is far superior to a blunt expensive one. Second hand chisels is another option.
In summary, start with some cheap chisels and sharpening system. Learning to sharpen and use them. Then buy individual good quality chisels to replace them as you find their short coming (need a good bevel edge for dovetails for example). Oh and upgrade the sharpening system as you go.