Hi Rose, no one else has replied so whilst not a legal expert I will advise you as best I can.
I certainly would include a contract/terms and conditions as part of your proposal.
Firstly keep things simple, limit the terms to as few as possible whilst covering everything. That may sound obvious but some companies I have worked on behalf of have had their t's & c's over 4 pages. Another on just the one.
A framework is as follows:
You need to mention whether your price is subject to VAT or not.
Explain the invoicing period (calenday monthly, 4 weekly) commencing upon first day of service.
A payment due date - such as 28 days from date of invoice. You also need to state what will happen in event of late payment - suspension of service, a charge for every phone call/letter as a result of late payment etc.
When the invoice will be sent (the industry norm is usually at the beginning of the invoice period - not at the end - otherwise you will get into cash flow problems).
Explain what will be included - usually the chemicals/materials to do the job. Toilet rolls, hand towels, refuse sacks and bin liners etc are usually rechargeable or will be supplied by the client.
How long your quotation is valid for (3 months is reasonable - any longer gives you the entitlement to adjust your costs - taking into account the ongoing increase in wage rates).
How long you are to hold your price for (typically 12 months).
You need to cover whether Bank Holiday working is included or whether any such days worked are charged at an additional cost. Beware Xmas Day, Boxing Day, NYD - charge a significant premium for these - you need to ensure that you are paying a high enough wage to entice your staff in on such days if they are needed.
A notice period of contract termination (1-3 months and written) on either side - and that you reserve the right to charge the full amount for any period not given. For example if you state 3 months and the client only gives 1 month they must pay you the full amount for the 2 months differential. If you do not cover that the 3 months term may be deemed invalid by the courts, or you may only get the profit amount for that period.
A paragraph covering site closure such as the summer shutdown (you will continue to invoice as if normal service was provided).
You need to state that the client, their staff, or any other contractor is not allowed to use your equipment or materials and that any damage or repairs (and subsequents costs) if it does happen are the responsibility of the client.
Most importantly, you need to indemnify yourself against any additional costs incurred through the TUPE regulations. If you are not aware of TUPE I suggest you find a different industry to work in. This may seem harsh but to those of us who have worked in the industry for a number of years TUPE is still a minefield - I believe that the maximum fine for breach of these regulations is £25k per person involved!
If you do not ask for a signed contract you will need to state that engagement of the service is deemed as acceptance of the terms.
As I mentioned at the beginning, I am not a legal expert and whilst the above should cover most eventualities it needs to be dressed up a little more in 'legalese'.
Perhaps other readers could add any further comments/clauses that they feel should be added.