Because Waterlow Court is a listed building, an EPC isn’t required because any possible improvements may be limited by the listing. For example, the windows are single-glazed leaded glass and cannot be replaced.
However, many of the flats that have been surveyed reveal the same ceiling on improvements – the single glazing, and the lack of cavity wall insulation – limiting the potential rating to a C or D.
Some of the flats have had secondary glazing fitted, and you may wish to do the same with flat 1, though it would be advisable to seek listed building consent before you make any alterations.
The quickest improvement you could make would be to upgrade the thermostat controls.