A US firm, GEO Group, recently took over Campsfield House

A spokesman for the Campaign to Close Campsfield said 80 detainees began the protest on Wednesday morning and another 40 have now joined them.

The protest group claims detainees at the centre near Oxford are being "treated like animals".

The Home Office said detainees were treated with "humanity and dignity" and it was monitoring the situation.

A Home Office spokesman said: "The latest situation at Campsfield House is that no detainees have refused food for three days or more and only two detainees did not eat the evening meal yesterday.

Once you are put in here, the immigration service forgets you Campaign to Close Campsfield

"The number of detainees who have missed breakfast and lunch today is not uncommon. At all the centres there are facilities available to purchase food, and some people choose to take advantage of these.

"The welfare of detainees is of paramount importance to IND (Immigration and Nationality Directorate), and all detainees refusing food are closely monitored to ensure they receive all appropriate care."

In a letter distributed by the Campaign to Close Campsfield protest group, the detainees say they are made to do odd jobs for officers, some of whom - the letter alleges - make "racist comments" towards them.

The letter states: "Once you are put in here, the immigration service forgets you."

Less than a month ago, Florida-based firm GEO Group took over Campsfield House, which has a total capacity of 198 male detainees.