Okay all, an update. In the end went for a pair of Castelli Polare 2 Bib Tights (
https://www.castelli-cycling.com/gb/polare-2-bibtight/p/451352319A), not cheap by any stretch of the imagination but they ticked all the boxes and I'm a tend to buy it once, buy it right and hang onto it type bloke.
After three and bit months of use, including some very cold rides (well cold for the UK) I'm really pleased with them, warm, dry, windproof and breath very well. All in, does what is says on the tin.