Its too early yet - down in Farnham, Surrey, I'd see this in flower in May, warmer areas it might be April, so depends where you are and how cold or not spring is. What feed have you been using?

We are close to Cambridge and there is a big banksiae, obviously well established, in the grounds of a local garden centre (where we bought ours) and that has flower buds and a few blooms that were out a few weeks ago - obviously confused by the weather this winter.
I may well be worrying too soon as the weather has been strange and a lot of other spring flowering plants and bulbs in my garden are not behaving as usual.
We have fed the plant with organic pelleted poultry manure - not the best idea?

Probably not - on the assumption you dug the area over and added (hopefully) composted manure before planting, no feed should really be necessary. Sorry, going to get a bit technical now! The trouble with pelleted poultry manure is the nutrient level is fairly low, but it has double the nitrogen to any of the other ingredients, so an NPK of around 4-2-2.5, nitrogen being the first figure, and nitrogen encourages leafy growth in particular. With a specialist rose food such as Toprose, the NPK is 5-5.5-12, so you can see the last figure is much higher (the K stands for potassium).

You'd probably be better to use Growmore pellets, with a balanced NPK of 7-7-7, rake or turn them into the soil, then mulch over the top, at the base of the rose with composted animal manure, particularly if you didn't add manure before planting. Or at this stage, just mulch with the composted animal manure if you didn't enrich the soil beforehand, but not allowing the mulch to sit against the main stem.

As for flowering times, RHS states April/May for this particular plant - the variation is to do with the weather in a particular year, and the micro climate around a particular plant, so a mature one planted against a south facing, sunny wall, in a sheltered spot in a warmer part of the country is likely to flower much earlier than one not in such a situation.

More info here

http://www.crocus.co.uk/plants/_/rosa-banksiae-var-banksiae/classid.1161/

And there are two clones about, one of which is much more reluctant to flower. We got rid of the one we had as it never managed to produce a bloom in 5 years.

Thank you both for your comments and information - all really useful.

I bought mine two years ago too. I heard about it on gardeners question time. Mine did not flower last year either. It has put on growth and hopefully will get some flowers this year.

Like most species roses, it only blooms on last year's growth. If any serious pruning was done last fall or winter, then few, if any, blooms would develop now. Frost damage could have the same effect.

That is good to know. I did not prune mine more by lucky accident than knowledge.