Breaking the top off tomato plants?

I am growing tomatoes among other plants f the first time this year. One of the plants has become as tall as me and it has almost reached the roof of the greenhouse. I have heard that if a tomato plant becomes too tall you should break the top of so that it will focus on producing fruit. What do you think about that?

 

Will breaking off the tip produce more trusses or will it stop more being produced? Mine never get tall here, possibly 4 foot tall.

 

I live in London and I bought them one and half months ago when they were small plants. Thanks I will go ahead with that then.

 

The other option is to "layer" them, rather than take the growing tip out.

I don't "stop" mine until one month before I expect first frost in the Autumn. If they hit the greenhouse roof before then I train them in some way (some years by layering them) to give them some more growing height / space.