Is a SRA a valid let down aid
Yes, its Radar
See Stds Doc 25
Instrument Approach training
Applicants are to be trained in at least 2 instrument approach procedures using VOR, ADF, ILS, GPS, Radar or VDF (of which at least one must be pilot interpreted). Completion of a notified, recognised civil, or military, instrument approach procedure during training must be certified in the applicant's flying logbook. In this context, ‘notified’ means that the approach procedure is notified by the Authority in the AIP or by the UK Military or the appropriate aviation authority (if not in the UK) in their equivalent publication.
Note that GPS approaches are defined as those notified as above and flown using equipment certified for the conduct of such approaches in the aeroplane’s Pilots Operating Handbook or Flight Manual; overlay approaches or privately designed approaches are not acceptable.