Do self-test systems still require annual contractual maintenance? Fire Service enforcement officers always ask for proof of contractual maintenance and testing of emergency light systems

That would depend on the installation type. Where the lighting is part of a central testing system or is an addressable system powered and tested from a central source then there are technical elements that require external maintenance one or two times a year.

If they are just a large quantity of self contained self testing units then as they carry out the monthly and annual tests in theory you don't need anymore than the monthly walkaround to check the visual indicators and for any damage with the wiring side checked in the 5 year EICR.

The law only requires "A suitable system of maintenance". Keep a log of monthly checks and manufacturers data showing these are self testing and the system of maintenance doesn't require the traditional service visits and you are legal regardless of what a fire officer, used to standard fittings, wants.

Of course of the manufacturer's data requires a service (such as with a central system) then that's what you have to do.