British manufacturing was in free fall in the 70's, the gun trade was one of the casualties. Fantastically high tax rates and cost of labour was the final nail when added to lacklustre management and investment.
Gone were the monopolies of yesteryear when anything made sold.
Lack of imagination and the view pile it high and sell it cheap just didn't cut it with those with disposable incomes wanting more. More was a better trigger and accuracy, which British gunmakers weren't delivering. Far too much relying on old tired designs, or looking for ways to cost cut and use old machinery.
The Spanish and Italians took the shotguns.
The German's gave the rifles that took and utilised the new fangled Jap budget scopes.
Niche makers like Theoben and AA could make better mousetraps and they sold OK. English "Best" rifles and shotguns have never been bettered though many have tried, but they are eye wateringly expensive (so are Prada handbags.)
For the collector then the late 70'a and 80's are a most interesting time. Time of change are. Great fun collecting and seeing what went on. There are a good few rifle to be collected, but not an outrageous amount. Used then few cost much. Mint in box then those are demanding a real premium.
Its certainly fun chasing down good examples.