I spent the day with Grimsby's cup heroes ahead of their clash with Brentford - this is what makes the Mariners special, their manager's uplifting rule for training and the inside story of how they shocked Man Utd

Every father wants to ensure their child's requests are granted but there are occasions when such requests leave a father in an extraordinary situation.

So it was for Kieran Green, Grimsby Town's proud captain, who found himself outside a solemn Manchester United dressing room, waiting to speak to Bruno Fernandes – who, moments earlier, had been rocking on his haunches in disbelief – on behalf of his 11-year-old son, Deacon.

'All he'd said to me before the game was, "Dad, can you get me Bruno's shirt?". So what could I do?' Green asks, as we talk at Grimsby's training enclave about the tumultuous August night that reminded you of sport's wonderful possibilities: a 2-2 draw with one of the world's biggest clubs before a 12-11 victory on penalties.

'I'd never really swapped shirts with anyone before but that was the one Deacon wanted. Do you know what? Bruno was brilliant. I've got a mate who is at Newport; they'd played United in the FA Cup a couple of years ago and he told me that Bruno would surprise me.

'You have this impression, if you've only seen him on TV, that he can be short-tempered or moan a bit but it couldn't be further from the truth. He's such a good bloke. We've just knocked them out of the cup and there he was, giving me his shirt and wishing us well.'

As is everyone. Grimsby entertain Brentford tonight, aiming to reach the quarter-finals of the League Cup for the first time since 1985 – a run in which they knocked out eventual League Champions Everton at Goodison Park – and they will carry the backing of all neutrals.

The odds are against them, of course, but this is a story about hope, revitalisation and the pursuit of a dream.

For in the fallout to that second-round tie, when Grimsby won the kind of dramatic penalty shootout that grips even those who don't like football, this proud club's huge feat seemed to be overlooked. Ruben Amorim's travails were one thing but what was it like for his counterpart David Artell?

Initially, it was a whirlwind. Artell lives in Chester, with his family, and crosses the Pennines most days to work. He'll do 40,000 miles a year behind the wheel, commuting and scouting, and the drive back that night resulted in him walking through the door at 3am; the adrenaline was rushing through his body so much, he didn't go to bed until 4:15am.

He was up again at 7am, his phone persistently buzzing with congratulatory messages. By 9am, he had done a round of interviews, started some analysis and his mind had flipped forward to that weekend's game against Bristol Rovers.

'But do you know what? I watched the game back three weeks later, as a fan, with no distractions,' says Artell, the kind of man from whom you walk away feeling better for the conversation. 'It was at that point I thought to myself, "Hang on – we've achieved something here. We were actually decent".

'I met a couple of elder gents, who have been fans for 50, 60 years. They told me that was the best they had ever witnessed. They'd seen the game at Everton in 1984 (Grimsby won 1-0) but they said this was different. Yes, it was fantastic and I was delighted but it's already been wrapped around someone's haddock and chips, hasn't it?'

In other words, it's old news. Artell is ambitious and wants to look to the future, hoping that the football club can be at the heart of regeneration in the area – the historic Cleethorpes seafront is currently being revamped – and something of which the local community can be proud.

He's certainly doing his side of the bargain. When Artell, who during his playing career represented Gibraltar seven times, was appointed two years ago, Grimsby were in a rut, looking over their shoulders and fretting about a future that might feature the National League.

Now, though, the landscape has changed. Plans are in place for them to move to a new training ground in two years and the squad has that priceless ingredient of being in it together – the club bought three houses on the seafront and in each of those, four of their players lodge.

'The owners (Andrew Pettit and Jason Stockwood) have allowed me and the chief executive (Polly Bancroft) to implement things,' says Artell, whose recommendation for haddock and chips is Ernie Becketts on Market Street. 'We have a group of players that want to get better; when you come into work, knowing that you are not going to get shouted at, you learn things.

'It might be "how many calories does a sumo wrestler eat?" or something completely random to start the rondo! Basically, we ask a question and whoever gets it right, gets given the ball and they start the drill. It just breeds a culture of wanting to get better, wanting to improve as footballers.

'Before you know it, the environment is such that they are staying here until late in the afternoon. If you go into work smiling, you'll thrive. That's why we are investing in the players.'

It's paying off. There was a hiccup at Artell's old club Crewe on Saturday, when Grimsby were beaten 3-2, but a promotion push is realistic and there was nothing fortuitous about them eliminating United then Sheffield Wednesday.

Grimsby represent all that is good about English football and while Artell isn't keen on raking over the success that has put them in the spotlight, his captain provides an insight into the team talk that preceded a shootout that went on so long it delayed the News at Ten.

'The gaffer came onto the pitch and, straight away, he settled everyone down,' Green, who arrived at Grimsby after spells at Halifax, York and Blyth Spartans, explains. 'He told us: "You have won already. This is a night that will be remembered forever." That took a lot of the pressure off.

'It was the right thing to do at the time and it was just what the lads needed. I think that night, everyone was a Grimsby Town fan if you didn't support Manchester United. Lots of people my age (28) were brought up along the lines that if you didn't support United, you hated them.

'It was something incredible and I'm not sure it's sunk in properly, even now. Things have changed a bit. I'm being inundated with ticket requests but the great thing is everyone is interested in what we are doing. This is the reason we play football – these are the games you want to be involved in.'

There will be another on Tuesday, with the stadium sold out and expectation going through the roof. Can lightning strike twice? In many ways, Brentford will be even tougher opponents than United because they won't be walking blindfolded into an ambush.

'But this is a two-horse race and we only have to win by a nose,' Artell reasons. 'If we lose, I will shake Keith Andrews' hand and show the humility in reverse that I did to Ruben Amorim. But what a time it is: Brentford then Ebbsfleet in the FA Cup at the weekend. It's bonkers.'

And, actually, quite brilliant.