On a 52 plate it could be a 90, 110 or 130 bhp diesel.
You could do worse than to look at the
badge on the boot. If the TDI has a red I then you can expect the engine to be 110 bhp. If it has a red D and a red I then you can expect 130 bhp.
Of course this is just a
badge, and people have been known to change the
badge as a sort of cosmetic upgrade. But it is a start.
Other than that, we really need to know what engine is inside the bonnet, by finding out the engine code.