You could get a carer through an agency. If so, you'd have the advantage of not having to worry about tax and national insurance. You'd also automatically get cover supplied when your regular carer was sick or on holiday. The disadvantage of doing so, however, is that it will cost you quite a bit more because the agency will have to take their cut out of what you pay.
HMRC take a dim view of people claiming to be self-employed when they're working on a regular basis for just one employer. So if you engage the services of a full-time carer (other than through an agency) you would need deduct PAYE and National Insurance. See here:
http://www.theanswerb...n/Question924227.html
You'd have to ensure that the carer received a minimum of 28 days paid holiday per year and that their shift patterns complied with the relevant legislation:
http://www.direct.gov...sAndTimeOff/index.htm
With regard to insurance, see here:
http://www.hse.gov.uk/pubns/hse40.pdf
Chris