About agencies and self employment
If you do engage the services of a self-employed PA / Carer you must be sure that they have been granted self-employment status by HMRC, otherwise you are liable for their tax and National Insurance.
Bear in mind that if they are self-employed in another capacity (i.e. painter-decorator) this does not mean they are self-employed as a Carer. Self-employment status is granted by occupation rather than per person. If you mistakenly employ somebody thinking they are self-employed and it turns out they are not, you will be liable for all back-payments of NI and PAYE contributions plus fines.