Corporal Roberts, 32, from Hemlington was killed by enemy mortar fire in Helmand Province.
The father-of-three will be honoured with a full military funeral.
At the opening of the monthly session of Home Office questions in the Commons, the Home Secretary paid tribute to the late PC David Rathband.
On the day of his official memorial service in Newcastle (which the Police Minister Nick Herbert is attending), Ms May called him a brave and fine police officer. She added that his death was a huge loss to the Northumbria force.
Derek Proud reports from The Cathedral Church of St. Nicholas in Newcastle.
Former colleagues of PC David Rathband will pay tribute to him today at a special memorial service organised by Northumbria Police.
Hundreds of mourners attended his funeral in the Midlands at the weekend. He grew up in Stafford with his identical twin brother Darren.
The father of two was shot and blinded by Raoul Moat in July 2010. He survived and went on to set up the Blue Light Foundation which supports people in the emergency services injured whilst on duty. And he raised thousands of pounds for the charity, taking part in the London Marathon last year.
He also published a book called Tango 190.
He was found dead at his home in Blyth last month and leaves behind his ex-wife Kath and two teenage children.
This afternoon's service will take place at St Nicholas' Cathedral at 2 o'clock.