Do you know the UK law re recruitment ?
If not read it -
https://www.gov.uk/government/publi...employment-agencies-and-employment-businesses
You may also want to look at the REC (Recruitment and Employment Confederation) who have guides for recruitment start ups. What sectors are you planning to cover, are any regulated industries, will you come under the gangmaster licencing rules as well. Are you doing temp or perm, how about Umbrella ? Have you sorted insurance ?
Having done 27 years in mainly perm mainly IT recruitment, I will tell you now that cashflow is the big killer if you go down the temp route,
Imagine this
You put a temp out to work at a company starting yesterday, they will give you a timesheet this Friday and you will run a payroll next Mon/Tue with the money leaving your account on Tuesday to appear with them on Friday (this is normal, deviate from it other than quicker and you will lose business immediately).
You will invoice the client on the Tuesday as well, they will take at least 30 days to pay. If they don't you have still paid the temp (that is law). A standard rate would be £10 to temp / £15 charge, that will actually cost you a bit over £13 once you have accrued for holiday pay, pension and employers NI so you will be making abut £1.75ph. 4 weeks of 37.5 hr week will make you £262.50 (if the temp works every day and doesnt have any days off) but during that time you will have paid out 4 weeks of pay (at £375pw gross so over a grand Net)
Now, imagine you get a contract to put in 20 temps somewhere - even ignoring any bulk discount or longer payment terms, do you have the capital to finance the cashflow needs of that ?