Image caption Paul Hill, seen here on his release 25 years ago

In October 1989, the Guildford Four were released from jail. Their convictions for blowing up two pubs in the Surrey town during an IRA bombing campaign had been quashed.

One of the Guildford Four was Paul Hill, whose 15 years in prison are documented in letters he wrote to his family and later donated to the Archive of the Irish in Britain, at London Metropolitan University.

The letters reveal Mr Hill to be by turns funny, angry, rebellious and despairing - but always articulate.

In 1974, Paul Hill was a 20-year-old Belfast man living and working in mainland Britain. In October of that year, the Provisional IRA planted time-bombs at the Horse and Groom and Seven Stars pubs in Guildford, killing five people and injuring many more.

A few weeks later, he was arrested in Southampton, and became the first man to be held under new powers introduced by the Prevention of Terrorism Temporary Provisions Act.

Her Majesty's Prison Winchester, 12 December 1974

Image copyright London Metropolitan University

As you know I was at court today again, but I was only there for a couple of "mins".

I seen some of the other people I was supposed to have did this with and will be back, up in court on Monday. Don't be worrying too much mum. As you know it will all be alright as it get sorted out in court.

Paul Hill, Gerry Conlon, Paddy Armstrong, and Carole Richardson all made signed confessions and were charged with the Guildford bombings.

All four would retract their statements, claiming they had been obtained using violence, threats to their family and intimidation.

"We were brutalised," says Mr Hill. "I was stripped naked and threatened with firearms and mock executions. I was told I would be thrown from a window."

Guildford Four Timeline

5 October 1974 - IRA bombs explode in two pubs in Guildford, Surrey. The pubs were targeted because they were popular with soldiers stationed at nearby Pirbright barracks. Five people (four of them soldiers) died

22 October 1975 - Paul Hill, Gerry Conlon, Patrick Armstrong and Carole Richardson - the Guildford Four - jailed for life at the Old Bailey

19 October 1989 - After years of campaigning, the Court of Appeal quashes their convictions, ruling them as unsafe, and releases them

9 February 2005 - Prime Minister Tony Blair formally apologises to the Guildford Four for the miscarriage of justice they suffered

21 June 2014 - Mr Conlon dies, aged 60, after an illness.

But all four were found guilty and received life sentences.

The judge told Mr Hill that he should only be allowed out of prison due to "great age or infirmity". The judge's only regret was not being able to have him hanged.

Paul Hill's girlfriend Gina was pregnant when he was arrested and he would not be able to see his daughter Kara outside a prison visiting room until she was 14 years old.

HMP Bristol, 26 October 1975 (days after sentencing)

Image copyright London Metropolitan University

Mum I was sorry to see both you and Gina upset. I know it is hard for you's to take. God knows what Gina must feel like...

She is the one person who knows I didn't do it. So if I feel like its the end, what must she feel like.

Some day mum people will find out the truth, but that isn't the point mum, I've been told I'll never come out of prison. How can I take that mum? I can't.

It would take all those years and a campaign supported by ex home secretaries, former law lords and international politicians before the convictions of Mr Hill and the rest of the Guildford Four were quashed and they were finally freed.

Find out more Listen to Archive On 4's programme From Inside: The Guildford Four on Radio 4 on Saturday at 20:00 BST and later on the iPlayer. Listen to the programme

"Think what you attained from when you were 20 to 35," Mr Hill says, as he recalls his time in prison.

"You got a job, met a girl, you grafted to get a house, got married, had a kid, watched your kid have its first day at school, have its first communion and grow up to be a young woman, I missed every single bit of that."

During his 15 years of incarceration, Paul Hill would be moved 50 times from one prison to another - "ghosted" in prison slang - with little or no notice and often in the middle of the night.

In this letter he describes being transferred amid great secrecy, from Gartree to Dartmoor.

HMP Winchester, 20 October 1978

Image copyright London Metropolitan University

A joke really mum, "top secret again" no one is supposed to know we are on the road, right cloak and dagger. Yet sirens blasting, lights flashing, horns honking. We wake up half the country from Leicestershire right though to Devon...

I only notice a dozen cars the whole way, one which was unfortunate enough to stop beside us in an all night service stn on the motorway for petrol, all the Clint Eastwoods jumped out of the cars pointing you know what at the car. The poor man and woman were petrified. I only want petrol he shouted. I thought don't tell the judge in the Bailey that mate, he'll give you life'. Im here for less than looking at them.

Mr Hill recalls: "At every opportunity and to everyone I spoke to I was always establishing the fact that I was innocent. I told them they had no jurisdiction over me whatsoever."

Slowly, campaigners on the outside uncovered new witnesses and forensic evidence that supported the Guildford Four's case.

One of the most compelling reasons to doubt the convictions came at the 1977 trial of the Balcombe Street gang, an IRA unit three of whom admitted in court they planted the bombs in Guildford and Woolwich.

But it would take more than another decade before they were released.

Wormwood Scrubs, 25 June 1982

"Northern Ireland have just scored in Spain! They have done really fantastic although I have the hump with them as George Best should be out there with them.

I hear I am on my life review board next month. The priest asked if I wanted him to do a report for me. I guess I'll have all the idiots asking the same. I shall tell them all the same, 'No, I have no intention of wasting my time with you people. I never have done and never will. Only my body is in prison, my mind is free. Your minds are in chains!'

Tell Martin and Marion to listen to The Message from Grandmaster Flash, it's very good and the words are really near the mark. It's almost the signature tune here.

Your ever loving son.

PS Ireland have gone out. PPS So have England."

Image copyright Getty Images Image caption Northern Ireland losing to France in the 1982 World Cup

Albany, 9 December 1988

Dear Errol,

The priest comes to see me and knows all about the case. He asks me how can I possibly handle this. He could learn a lot from my spirit I told him, I have people with spirit as good as my own who make it easy. Being innocent is no small factor either.

Anyway it's plain that this will never go away Errol. The calibre of the people supporting the case won't let it. But have we to sit and watch things come to light in dribs and drabs every so often over the years while our lives fritter away?

Your loving nephew Paul

In 1989, the home secretary referred the case back to the Court of Appeal and ordered a police investigation into the original handling of the convictions. The Court of Appeal found that police officers had lied to the original trial. The convictions were immediately quashed and the Guildford Four released.

Joshua Rozenberg, the BBC's former legal correspondent, says the appeal hearing did not allow compelling evidence supporting the Guildford Four to be publicly aired.

"The [Crown Prosecution Service] conceded immediately the case opened and the hearing was cursory in the extreme. That was very unfortunate because it meant that the case was not properly put in court," says Rozenberg.

Mr Hill says: "The most insulting part was when the judge said, 'At least something has been gleaned from this unhappy incident.' Well I can assure him that for me and for Gerry, Lord have mercy on him, and for Carole and for Paddy, it was more, much more, than an unhappy incident."

Image copyright other Image caption Paul Hill now lives in Washington DC

Gerry Conlon, another of the Guildford Four, died earlier this year, a loss that deeply affected Mr Hill.

After prison, he married Courtney Kennedy, daughter of the assassinated former US Attorney General Bobby Kennedy. The pair, who have since split, have a 17-year-old daughter.

He is now 60 and lives in Washington DC with his girlfriend, a senior producer with ABC television.

"I can walk out along the waterfront in Georgetown," he says, "I can go into any museum in DC, free as a bird, but with a little bit of me still hurt, still angry and a little bit of me that still dwells on something that was incredibly disturbing in my life."

Listen to From Inside: The Guildford Four at 20:00 BST on Saturday 4 October or catch it later on the BBC iPlayer.