Joey Barton has invited the authorities to "make him a martyr" after the attorney general's office said it was looking into his tweets over the impending John Terry trial.

"I will gladly go to jail for a month, in the name of free speech. I have no problem with what I said. Make me a martyr …" the Queens Park Rangers captain tweeted on Sunday.

The attorney general's office said it had been made aware of a series of robust observations made by Barton on the stripping of the England captaincy from the Chelsea defender following an allegation of racially abusing Anton Ferdinand during a match at Queens Park Rangers last year. Terry, who denies the charge, will stand trial in July, just a matter of days after Euro 2012 finishes.

Barton, who was playing in the match at Loftus Road in October, has defended his comments on the grounds of free speech. However, a spokesman for the attorney general's office said: "I can confirm the tweets have been brought to our attention and have been viewed."

Dominic Grieve QC is the current attorney general. He is the government's senior law officer and part of his remit is to make sure people facing criminal allegations receive a fair trial.