I would say that this is not just a UK problem. The state of the avionics in rental planes at KCDW, are if anything, worse: making instrument flight positively unpleasurable. For example, of the 2 PA28’s I fly, only one has a reliable VOR (just the one), but it doesn’t have a reliable DME. It’s the reverse with the other (ie an unreliable VOR, but a reasonable DME). At least with the warrior for rent at EGKH, the instruments are in reasonable condition.
The problem is not with the sad state of our aircraft construction industry, but the general cost of flying, and what people are prepared to pay for it – ie because the costs are so high, most of us are only prepared to pay the absolute minimum - which results in rentals with just the basics.
It is an interesting philosophical point that while the Yanks earn loads more than the Brits, and the cost of flying is easily half due to cheap gas, they too are only prepared to pay the minimum, which to us Brits is relatively dirt cheap…