I think the construction and use regs are a bit lapse with regard to trailer tyres, but I also think like everything you need to judge the risk.
Even though you are only 2 mins from the slipway you are technically travelling on the highway Illeagally.
The only time this would be a problem is if you have an accident on the way.
How busy is the road etc?
If it was me, and I lived two minutes from the slip, I think the police would be more interested in the fact that I had no light board, prop bag etc