Hello,
Wage/salary varies for FI(R).
£15 - £20/ hour, no retainer - most common ballpark.
£10/hour and daily retainer of £30 - common.
Salary (if you can negotiate one) is around £12-13k with £5/hour flight pay - average.
Demand is high in the UK for instructors right now (including restricted), especially with Cabair based at strips around London (£20/hr no retainer).
VFE.