Look at what you need:
A. Minimum Wage
B. Tax & N.I
C. Holidays
D. Any Bank Holiday Working
E. Overheads
F. Materials - mops,chemicals etc - usually 3% of wages
G. Profit Margin ( how much do you want to make at the end of the month)
If you are going to supply consumables, Toilet tissue, Soap, Paper Hand Towels - charge them as extras and add a perecentage - I add 25%.
If you are going to wash Towels/Tea Towels charge that as extra - depending on how many £3 - £5 per week
Hope this helps