would I have to pay tax if....

[Fio2]

I advertised myself to do odd jobs for people. Like shopping, cleaning etc. for elderly people?

Only if you earn more than the tax-free personal allowance (currently £4,745 per annum). If you are already an employee then anything extra you make via self-employed activities must be declared on your tax return and the tax duly paid.

no expert but I think "officially" you'd have to declare this for working on a self-employed basis, however, most casual labour is cash in hand so no real need to declare, sure most people don't. if you set yourself up as a company that would be different.

oooh be careful ..."No real need to declare" - actually you are required by law to declare all your earnings!!