Gatwick South was opened in 1958, it is today one of the best terminals in the UK.
Prestwick's terminal dates from 1964, neglected and to some degree, dated.
Glasgow's terminal opened in 1966, has IMHO the best security hall in the country, and does the job well with two airbridge served piers and a low cost one.
Edinburgh dates from 1977 and has been built out and modernised.
Now Manchester T1 dates from 1962, so what's happened is a neglect and de-investment based upon an end of life that has been extended. Older, contemporary options are in better condition due to continued investment. I get that end of life is in the plan, but to not invest in the basics just means the CX collapses even further. Comparatively, there are too many airports who manage to deliver the basics better, one of which is fellow MAG member, Stansted.