If you want to expand your business and you have regular contract work, there should be no reason why you simply cannot employ someone to do the work. Any bookkeeper or accountant can help you to setup a straightforward payroll system. Most people do not want the hassle of having to submit a tax return and would rather be PAYE employed. Whilst it is true that a lot of cleaning firms do use self-employed subcontractors, many of them only do it as a tax (and employment legislation) dodge. If you do this, there is always a danger that HMRC will not accept the self-employed status of your cleaners and send you a massive tax bill, possibly going back years, which could ruin your business. In general, if you have regular contract work and you tell the cleaners what to do and when and possibly supply equipment and uniform - it might be difficult to argue that they are self-employed. Some firms get around this by basically operating as an agency; they don't pay the cleaners directly - the client pays the cleaners and a separate ongoing fee to the agency for finding the cleaner.
The situation might be different if you undertake a lot of one-off deep cleans and subcontract the whole job to an independent cleaner - this is a very common practice. You should get professional advice based on your own situation and circumstances, but in general, if you want to build a proper bona fide business - employing staff is the best way to go.