Legally you can't hire his services while he is using your tools ie van etc
Hmrc are clamping Down on self employed working full time for one person ,
If you are the sole person he earns his money from and if he is using your tools
Then he isn't self employed ,
you can however employ a Subbie in simple words a window cleaner who has his own van and tools and he pays you a percentage of what he cleans pay him a percentage of what he cleans he invoices you and that's it,
A Subbie will however not work with you all the time they normally have there own jobs and they get paid more expect to pay a serious person around £150 per day but offer a percentage of work cleaned, also make sure you can pay him promptly that way he will take you seriously all the invoices is up to you to chase non payers etc