@JamesL - keep track of income and associated costs for your own personal reference, but not for anything more than that.
If HMRC decided to make a thing about referees, then referees could argue - in this gig economy world - that we should have basic employment rights from the leagues that we referee for (by the way, not a route I advocate in any way, but simply playing devils advocate). Part of those rights would be an expectation to earn the national minimum wage, which might mean...
Home to match: 30m
Inspection and warmup: 60m
Match: 105m
Post match activity: 30m
Match to home: 30m
Reports: 15m
Total time per match: 4.5 hours
NMW = £7.83/hour (at the eldest age group)
Minimum match fee = £35.23 + expenses.
Expenses. Lets say on average 10 miles each way = 20 miles at HMRC's 45p/mile = £9.00
So
total charge per match = £44.23
Not sure many grassroots clubs would support that!
But - HMRC would have to target each referee individually, and I don't believe the cost/benefit would be there - the time and cost investigating each referee would far outweigh the additional tax they could raise. I think for the foreseeable future we're safe to continue as we are.