TPS are in Bristol and I have a well used account with them - but unfortunately , as with many Golf Mk2 parts, the distributor 'was no longer available from VW since July 2015' - so they told me lats week!
In the end, GSF got me one, which I will be fitting soon.
For future reference and those who may be interested: (PB Engine, 8v, Digifant, 1991 model year)
The part numbers on the GSF one (Genuine Bosch, including cap, rotor arm, and hall sender) are:
0 237 520 044
On cap 0 986 237 638
and GSF part number is 920 VG 0110
It came in at just over £100 plus VAT plus a £40 surcharge which is refunded at any time in future (no time limit) when the old one is returned.