Was mentioned recently in a popular UK GA Forum, but can this be investigated please?Quite often in UK, especially when departing from smaller airfields, it isn't always possible to get a FPL activated in a timely manner.
If the departure airfield won't provide a FPL activation service then you have to rely on the, usually, very busy London FIR frequency.
If SD offered a FPL activation feature, with some kind of easily viewable confirmation message/status, then I think this would be a very good enhancement.