What are the alternatives?

Doing it yourself is not easy. It is difficult enough to master Inland Revenue tax tables with several tax bands currently in force. To add further complication, most nannies’ wages are agreed as net (i.e. take home) pay, while all tax calculations are based upon gross pay, never mind trying to become an expert in employment law!
Not declaring employment to avoid tax is a criminal offence which can potentially result in heavy penalties and career–damaging publicity. It also affects future pension and benefits entitlements of your employee under the National Insurance system. The Inland Revenue no longer turns a blind eye to this issue.
Just using an accountant is on average three times more expensive than using Stafftax. Add to that the cost of using a lawyer if the employment relationship turns sour and you could be looking at ten or more times the cost of an annual Stafftax subscription. That’s why even accountants and lawyers use Stafftax!