The 40-year-old said he was “massively surprised and just blown away by the support”.

He added: “When we set out on Tuesday morning for the first one, we were at about £40,000 I think. We set a target of £77,777 and we were a little bit concerned that we may not hit it. And then suddenly it just started to roll in.

“The support has been incredible. Rob’s felt it. I get a text off him every night (to say) how grateful they are of what this team have done.

“We’ve been really proud to wear the vest with number seven on, what that represents with Rob and his family, but also to have the MND Association on the front, to run in their colours, to understand the work that they do and the difference they make to so many families across the UK.

“Especially this week, I’ve heard so many different stories about how horrific this disease is. This amount of money will make a huge difference. It will change a lot of things hopefully. The awareness is crucial. We need to find a cure, don’t we.”

Sinfield came up with the plan only two months ago but completed each marathon in less than four hours.

He said: “Yesterday was the toughest by a mile. I did three in three (days) as part of my training at the end of October and that was pretty dark days, day two of that was the darkest I’ve probably been on a run.

“But during this I’ve been really energised. The team have been incredible, they’ve kept talking to me, singing, playing music. Yesterday was tough and a challenge but we knew we just had to get it done.

“When I look at the week, if you’d have said to me on Tuesday last week you’d get up on Monday morning, you’d have got six in the bag all under four hours, you had one to do, you were just short of a million quid and you’d be feeling the way you were feeling, I couldn’t have dreamt anything better.”

Sinfield won seven Super League titles and two Challenge Cups in a decorated playing career but put this achievement at the top of the list, saying it had been probably the most special week of his life.

“To be able to do something and help people, get the opportunity to make a difference, to raise over £1m for something that is very, very close to home when he’s a real good friend is really, really important and just the support has been immense and incredible,” he said. “It’s top of the list this, definitely.”

Some of the money will go towards ensuring Burrow’s family have a secure future, and Sinfield’s mind went back to a journey the two men made to see fellow MND sufferer and rugby great Doddie Weir last December.

He said: “We talked about what our team would do for him and a magic number we would try to get to to make sure the family were safe and he was comforted and he didn’t have to worry about those sort of things moving forward.

“To be able to send him a text the other night and tell him, what we talked about back on that dark day in December, we’ll do that and more, gives us as friends great satisfaction.”

The MNDA has been left stunned and delighted by the amount raised and attention will now turn to how best to use it.

Ian Gardner, head of development in the charity’s fundraising team, told the PA news agency: “There’s a huge amount we can do with it across all of our work – research, care, support, campaigning and awareness raising.

“Because we’ve just been so overwhelmed by this outpouring of generosity, I think we’re going to have to let Kevin get his breath back and then sit down and work out with Kevin and Rob and others exactly how we can best utilise that public support, how we can make sure that every penny of what Kev’s raised can really be used in the most effective way possible to take the fight to MND.”

Sinfield’s achievement has prompted calls for a knighthood, but he said: “It isn’t about that for me.

“The support has been incredible, but this has been about Rob and a group of friends, a group of team-mates, who have had some wonderful times together and now one of them has hit a rough patch and we’re coming out to help.”