I know you're in England and I'm in Tucson, Arizona.. but it's the 21st Century man. Hairlength shouldn't and doesn't seem to be an issue with most employers with perhaps the exception of those chronically conservative businesses such as banking, law firms, and 'big business'.

Can you pull it back and keep the sides combed in neatly? I did that for years and often folks didn't even realize I had long hair (down to my waist) until I turned my head.