Talking in pounds tends to distort things a bit, as the USD-GBP exchange rate is quite influential on UK pricing. Adjusted for inflation, the GTX 280 was $950. Then the 480, 580, 680 all launched for an adjusted $700-$750. The GTX 780 was $870 after adjustment. The GTX 980, $730. The 1080, 2080 and 3080 all launched around $850. So the average price for an *80 class GPU was maybe about $800 in today's money, with typically up to $100 of variance. It was the 4080 where prices started to shift, launching at almost $1,300 (when adjusted for inflation). And now the 5080 lands at $999. Expensive, but not utterly ridiculous.
Even if you look at mid-range, the 1070 was $379, which is $495 when adjusted for inflation. So the *70 class pricing has only gone up by $54 in real terms.
The real robbery is the degradation of performance in each series. The 5080 is not even remotely close to offering the expected performance for a next-generation *80 class card. Really, it's the 5070 Ti bumped up a tier (~30% improvement over the 4070 Ti Super). With that trend likely to continue down the stack, that means expected *70 class performance is likely to be found at $750, which is $255 over the inflation-adjusted price for a 1070