How can an electoral system that gave the Tories landslide majorities in 1983 and 1987 be favourable to Labour?

Given that there are now only 59 seats in Scotland rather than 72, that should help the Tories. So why do they insist that the system favours Labour, when in fact the English seats are still more or less the ones they left in 1997? Does this claim not admit that FPTP does not work and does not make all votes of equal worth no matter where they are cast? Could the Tories win in urban areas by offering something for people there to vote for? They still seem to struggle in places like Manchester, Leeds, Hull, Glasgow, Edinburgh, Liverpool etc. In decades gone by they used to get a good return of seats in all those areas.