you need to talk to an accountant before you start. I was an instructor during 1995/96 in addition to other employment, just last week the National insurance contributions office have come back to me looking for £8+ per week for the full two years I did instructing ( even for months when I earned nothing from instructing) I had always done my tax return and paid my debts promptly so this bill is a bit of a shock. Since you will probably have to pay similiar you need some sort of retainer for turning up, unfortunately I didn't.