What, if you wear a thermal base layer, interested in pants only, do you use for cold weather riding?  Ones I've got are buggered and wondering what to replace them with if any experience on here?? 

The cold on a bike is mostly the wind chill.I wear leathers so the legs don't get cold.If you wear jeans etc. using rainproof overpants (wet weathers) will keep out the wind chill on extremely cold days.The hiking camping stores have woolen unders if you don't like the look of wet weather pants over your jeans (but they won't negate wind chill if you have a naked bike).

I've got a couple of pairs of Kathmandu ultra core, worn under jeans do the trick. 

Thanks Keith. Have a store not far away. Will go for a look tomorrow 👍

I haven’t seen a pair with a fly , but l will be looking next time l buy a pair. 

If you're a cheapskate, Aldi has a sale on merino thermals, tops and pants, every July, stuff is about half the price of Kathmandu's. I've got both, Kathmandu's quality is slightly better.