Right, I'm back, with some test results and another question.

I've done two test pieces on spare board (that was taken up during
renovations upstairs), one with Ronseal Diamond Hard Floor Varnish
(water-borne polyeurethane, medium VOC), and the other with Wickes
Professional Interior Varnish (solvent-borne polyeurethane, high VOC).

As predicted, the Ronseal lowered the colour ever so slightly without
really changing it, but left a plasticky-looking finish that I don't
like at all. The Wickes produced the lovely golden colour that I was
after. However...

The management has decreed that the more natural colour obtained from
the Ronseal is to be preferred. In fact, she's right, as it matches
the natural wood colour of our stripped and waxed doors (the mellow
golden colour worked in the previous house, because the doors
themselves were a mellow golden colour, through the application of
linseed oil, which is not the case here).

So I'm tempted to use the Ronseal as the first couple of coats, to
seal the wood with a lighter colour, then to finish with a couple of
coats of solvent-borne matt (or more likely satin), to avoid the
plasticky finish. Does anyone know if there could be any problem with
applying a solvent-borne varnish over a waterborne one, once the
latter has dried? I can't immediately see that problems are likely - I
know you have to be careful if doing it the other way round, to make
sure the solvent has evaporated, but the water evaporates quite
quickly. Could there be issues over the one bonding with the other?

Regards
Richard