The pair were cellmates in a Cairo prison in 2014, held on bogus terrorism charges.

Peter was released in 2015, but Alaa remains behind bars.

It's hoped Peter's strike will pressure the UK government to act on Alaa's behalf.

Greste told The Project that he chose to join Alaa’s mum, who is also participating in a hunger strike.

“He was due to walk free on September 29 last year. His mum started a hunger strike on that day, because he should be out and she is protesting very forcefully and I felt it's the right thing to do to join it.”

“There's a lot of pressure that's building up. The timing is everything,” Greste explained.

“It's one of the things that Alaa made very clear to me, the timing around hunger strikes is

really crucial and it feels like now is the right time to step up the pressure. We think there is a chance he might be released and I want to be part of the campaign.”

Greste hopes to see his friend “released in the next few weeks”, but understands that “campaigns like this never depend on any one thing, any one action, it's an accumulation of pressure… and so what I'm doing is really building that pressure. It'll work eventually. We don't know when.”