It'd be interesting to see a comparison between that map and the map in the last set of local elections in which the Tories did comparably well. I'm not sure when that would have been though: probably one of the last set of the two-tier council elections but the smaller wards and different voting systems would skew things
1982 regionals probably, in which they also took 25% of the vote. It was FPTP and not all wards were the same size, wards in Glasgow were 6 times larger than those in the Highlands