Hi this is my first time on this board. Hello.

The above title is pretty explanatory, happened in my home today. Why should this be? I have run the cold tap downstairs to see if it will run dry but it is fine. Hot OK too. Happened this morning. Thames water have no cut offs. Any takers?

What's, "Thames water have no cut offs." mean?
The first thing I would do is shut the water off to the house and open up a upstairs cold water supply line. Then I wouls hold a bucket over the open line and have someone turn the water back on to try and flush out the cold water line. Speaking of lines, what's the material yours are made of? You don't have a Pex System with plastic tubing do you? Let me know, Tom

Thanks, I mean that Thames Water supply have not shut off the water in this area today, so it is not them that is the problem.. thanks for your advice will give it a go soon..

Hi let you know I have got it sorted. Did what you suggested. Seems it needed burping. Many thanks.