Let’s get the grim statistics out of the way first.

Norwich City’s ignominious FA Cup fourth round defeat at the hands of Luton Town made them the first top-flight club since Birmingham City – beaten by Altrincham in 1986 – to be knocked out of the competition on their own ground by a non-league side.

It was also the first FA Cup victory by a non-league club over top-flight opponents, home or away, since Sutton United beat Coventry City in 1989.

For those who believe that football did not begin until 1992, Saturday’s defeat also made City the first Premier League club to suffer such a fate.

And as fans who have been watching the Canaries for well over half a century may recall, it was their first exit from the competition at the hands of a non-league team since Bedford Town won 4-2 at Carrow Road back in November 1956.

That match was played with the club in the grip of a financial crisis that nearly put them out of business, in sharp contrast to the TV millions they can enjoy today, but if not exactly in crisis, City – and certainly their fans – are currently experiencing a deep depression that seemed inconceivable six weeks ago when they moved into seventh place in the Premier League table with victory over Wigan.

It is not just the fact the Canaries have suffered yet another Cup exit on home territory that will worry fans most, nor even the embarrassment of losing to a team 85 places below them on the domestic football ladder, as much as the fear that the stability restored by manager Chris Hughton and his players during that golden autumn run of results has been all but lost in a winter of increasing discontent.

What began in December as a series of brave, narrow defeats against some of the Premier League’s high-fliers has given way to sub-standard performances such as the capitulation at Liverpool and humiliation at the hands of the Hatters.

With City needing at least four more league wins to feel a measure of security, there will have to be a substantial improvement at both ends of the field – they have now gone 290 minutes without a goal.

As in the previous round at Peterborough, Hughton rang the changes, making six alterations to his line-up from Anfield. But whereas Posh were swept aside with ease, Luton were made of sterner stuff and few of those fringe City players given a chance to stake their claim for more regular senior football made any real impact.

There was far too much sideways movement and far too little forward thrust, and when City did find a way through the Luton rearguard, they found Norwich-born goalkeeper Mark Tyler in determined mood on the ground where he used to stand on the terraces on a milk crate.

It took 28 minutes for either side to muster a worthwhile chance, Elliott Bennett putting Simeon Jackson away but Tyler making a fine save, with the recalled Andrew Surman’s follow-up effort blocked by Luton skipper Ronnie Henry.

On-loan striker Harry Kane struck a low shot that Greg Taylor managed to divert wide, but the Hatters had a lucky escape four minutes before the break when Leon Barnett headed against the post from a David Fox corner and, as the ball rebounded back off Barnett, Alex Lawless cleared off the line – though TV replays later suggested the ball was over, echoing the City players’ vain appeal.

Russell Martin sent a lob just the wrong side of the post on the stroke of half-time, but the Canaries’ lack of punch saw Kane replaced by skipper Grant Holt from the restart.

Ten minutes into the second period, the change almost paid off, Tyler making a point-blank save from Holt’s header after Jackson played the perfect cross into his skipper.

Defender Janos Kovacs volleyed a cross from Martin dangerously over his own bar before a flurry of changes on both sides – but it was Luton’s three substitutes, rather than City’s Wes Hoolahan and Anthony Pilkington, who were to play the decisive role.

First Lawless, whose goal had knocked out Wolves, volleyed just wide from a touch by one of the newcomers, Scott Rendell.

Then, with 10 minutes left, the three Luton substitutes combined perfectly as Stuart Fleetwood sent J J O’Donnell racing away on the left and his cross was knocked in by Rendell, getting ahead of Ryan Bennett at the near post.

Luton’s dream victory might have been snatched away from them in the dying seconds of stoppage time had referee Andre Marriner spotted a clear handball by defender Lathaniel Rowe-Turner in the penalty area. Even at well over 100 yards’ range in the Press box, it was crystal clear.

It was argued by many observers that City did not deserve a replay in any case – but one would still like to see the rules applied.