what is this please

this has been growing on our allotment in the grass as it hasn't been rotavated yet.

 

It is one of the clovers, possibly the one the farmers grow for nitrogen fixing and animal food. Rotovate it in to increase the nitrogen in your soil.

 

that sounds like it will be useful
Thanks for the ID

 

Looks like Red Clover (Trifolium pratense). It's a wild, native species, but as Palustris says, it's used as a green manure crop. Famers where I come from used to turn animals out into the fields quite often, too, before ploughing it in. Rather strong, woody stems though, so it can be a bit of a problem to shift from a lawn! It tends to lie flat under the mower if it gets too big!