if a plant has been stressed they often flower in the hope of setting seed before they die. perhaps the roots were more damaged than normal or the sudden warm spell resulted in yes water at the roots so again the plant got stressed. Pinch the flowers out so they don't set seed and keep them well watered. hopefully they will put on growth later in the season.

In my case, it seems to be another one of those funny years for sweet peas.
I have got probably the best looking plants i've had for a long time, they are about 4 foot tall, but I haven't had a single flower.
Plenty have formed, but they have all fallen away.
Only now are they starting to produce decent buds.

As to the questioners problem, it would be useful to know when the seeds were sown, variety, and what the root system was like when planted out.
Depending on the reply, Seaburn won't be far out with her reply.

To get the best sweet peas, you have to sow early, overwinter in a cold frame, and get them planted out by the end of March.

Thank you for your helpful comments, the root systems were healthy Seaburngirl ,the variety are a mixed selection from a Wilkinsons or B&M 5- 6ft ers I think, sowed when Gardeners World did theirs in early spring , could be like said a funny year Srumpygrat,I will see how they go , I hardened them off as usual maybe I am too cautious, anyway thank you for your help

Good old gardeners world.

Did you pinch out the growing point at about 3 pairs of leaves?

The trouble with starting sweet peas off in spring is that they grow to fast and don't get the nice root system that slow winter growth gives them. If you think your roots are good, you should see the difference with the over wintered ones.
If you can't over winter, seed sown early February will produce reasonable plants. I can't comment if gardeners world start them off later than that.