Morning all,
Thanks for all of the helpful replies and comments on this topic, they really were appreciated.
I can now confirm that the A610 Heater Matrix is a Renault 21 item, in fact I recently acquired an old R 21 matrix and removed my matrix last night and they are identical in every way. In fact it looks like the whole heater system is Renault 21 from other photos I've seen.
It looks like my Matrix had been leaking for a long time and the leak was all around where the the metal parts of the matrix were crimped on to the plastic head unit from all the build up of dried crud in this area. In addition the slot where the matrix sits was wet through with old Type D coolant but luckily this is all plastic and in the base of this there are three small drain holes that feed out into the main drain hole underneath the heater unit itself.
Part Numbers are, Alpine: 60 00 009 307
Renault: 77 01 032 298
Valeo (the original manufacturer) : 883972
I trawled the internet looking for a Valeo one and they're just not available...for right hand drive cars that is, there are plenty for left hand drive Alpines but these are of no use as the inlet and outlet pipes are angled the wrong way.
There are a couple of right hand drive ones ones on E Bay from German companies but the postage charge is nearly as much as the item (search for item NRF Heater Matrix 58621)
Eventually I found a German company with, I think a UK arm: buycarparts.co.uk
They list R21 Heater Matrix's from 4 manufacturers but again, the only one they have is stock is an NRF one, cost including VAT and Delivery is £33.38 with a 3 to 5 day delivery window so I've registered with them and ordered one.
I'll post some photos as soon as I receive the new one, this is (hopefully a link to the sales page):
https://www.buycarparts.co.uk/nrf/2391895Cheers, Barry