For Scotland, the numbers told a grim and gloomy story. Two successive 3-0 defeats, one point from a possible nine – and that from a home match against Lithuania – had left Gordon Strachan’s side facing yet another qualifying failure.

Strachan himself seemed poised to resign. Indeed, he was widely reported to be considering his position even before the Scots lost heavily to old rivals England at Wembley in November.

But the former Celtic manager ultimately opted to stay on, deciding that the answer to his team’s malaise might just rest with his former employers. Strachan saw that the numbers at Celtic Park were telling an altogether different, more uplifting story, with Brendan Rodgers’ team en route to a historic ‘invincible’ domestic treble.

Celtic’s 2016/17 season in numbers
trophies – the fourth treble in the club’s history
defeats and 43 victories in 47 domestic matches
134 goals scored, 27 conceded and 26 clean sheets
106 Premiership points amassed – a new European top flight record
30-point winning margin over second-placed Aberdeen
118 years – the last time Scotland had an ‘invincible’ league champion

Such success would have been irrelevant to Strachan had it been underpinned by a clutch of big-money imports. But Rodgers had shaped his Celtic side around a spine of Scots, and several of those players were in the form of their lives. As such, when second-placed Slovenia came calling in March, the Scotland manager ripped up his previous selection policy – which relied mainly on English-based players – to start no fewer than six Celts.

It worked. The Scots produced their best performance in years and emerged with a hard-fought but thoroughly deserved 1-0 win. Their star player had been a Celtic midfielder making his international bow; Stuart Armstrong was later lauded by his manager for producing “the best Scottish debut I’ve ever seen”.

The gloom had been lifted, and Strachan admitted this week that he had taken a calculated gamble on “people who were feeling good about themselves".

"They bring that positivity to the squad,” he said of the Celtic contingent. “It was easy to pick those players, so easy. They’re on this run where they think they are invincible, which is fantastic. They are enjoying every game. Ask any of them if they’re tired just now. Tiredness only seems to creep in when you are getting beat.”

The Celtic sextet is made up of goalkeeper Craig Gordon, left-back Kieran Tierney, midfielders Armstrong and Scott Brown, winger James Forrest and striker Leigh Griffiths. While Forrest, having fallen out of Rodgers’ line-up of late, seems unlikely to start the return meeting with England on Saturday, it would be a major surprise if the remaining five were not retained.

“We know how each other play, there are partnerships there, confidence is high and we’re just not used to losing,” explained Gordon. “We go into games expecting to do well.”

Such belief will be needed more than ever against a star-studded England side that has yet to concede a goal in five Group F encounters. Centre-half Charlie Mulgrew admitted as much this week, describing Scotland as “massive underdogs” against the Auld Enemy.

But Mark McGhee, Strachan’s assistant – and a man who scored against England at Hampden in a 1-1 draw 33 years ago – believes the Scots' Celtic connection offers some hope. “Last time out, those six players brought a confidence and an understanding between each other which added something to the team,” he said.

“We saw their energy and their enthusiasm, and the confidence obviously, but there was another advantage too, in that you feel as if the players are connected. They have an understanding of each other’s game - the midfield players linking with Griff (Leigh Griffiths) up front, for example. That’s an attribute that is hard to bring that to a team when you have a week to work with them.

“England have great players, really top players right now," McGhee added. "They are in danger very soon of becoming a great team under Gareth Southgate. [But] it is not something our lads go into with any fear. There is a performance within us, no doubt about it, and that means we could get a result.”