To add to Daysleepers list:-
there are a number of "tests" the Revenue apply to see if you are caught under IR35 - it's a "balance" - not a majority taht decides
as above plus
4. Do you have an office/car/business card/pc/phone provided by your "employer"
5. Are you responsible for approving your own work
6. Are you on their internal contact/telephone list
7. Does the contract have drop dead date -and it should and better it should vary in length between engagements
8 Does the contract have an estimated value - it doesn't have to be correct at the end but it should be there
9 Avoid any mention of "roll-over" provisions in the contract
And if you avoid that then you worry about employing other sub-contractors yourself as you get caught by the Intermediaries legistlation