A senior police officer has urged Hornets fans not to let the disruption at Watford’s final home game ruin a “fantastic season”.

Both police and club officials have vowed lessons must be learned after crowd trouble marred Watford’s 2-0 defeat against Queens Park Rangers on Saturday.

The victory secured the West London club’s promotion to the Premier League and led to up to 150 fans invading the pitch at the final whistle.

Police horses were brought onto the field to hold them back as they celebrated, much to the upset of home supporters waiting to cheer Malky Mackay’s side during the traditional end-of-season lap of honour.

Hornets supporters, however, were particularly angry about the large number of away fans sitting around the ground.

And they were quick to express their unhappiness to the club, many leaving their thoughts on the Watford Observer website.

Picton84 wrote: “Pathetic attempt from WFC to keep QPR fans out of the home section. So much for being on the WFC database to get your ticket.”

HertsHornet said: “This is without doubt up there with one of the darkest days in WFC history and what makes it so much worse is that in mine and many, many others within the stadium, today is all the fault of the WFC board of directors with their disgraceful allowing of this to unfold. Family club - what a joke, I have never witnessed so many terrified kids in the Lower Rous as I did today.”

Supporter Howard Gillions wrote to the club to express his anger at how fans were treated during Saturday’s match.

He claimed his 80-year-old father was “assaulted” in the Rookery stand and several requests to eject away supporters were ignored.

He said: “I have decided that we will not be renewing season tickets next year. The events of Saturday were the final straw.

“Your treatment of the home fans compared to away fans is a joke.”

However, Brian and Jenny Graham, from Kelmscott Crescent, said they were “appalled” by the behaviour of some Watford fans towards away supporters.

They said: “In particular, the foul language and barely unrestrained anger was unedifying to say the least. What sort of example did this convey to the young children in attendance?

“The match itself was keenly played and Watford put up a good fight and can be proud of their success this season after the critics had us marked down for relegation.”

Chief Inspector Richard Harbon, the silver football commander in charge of Saturday’s match, said policing at Vicarage Road had improved “significantly” in recent years.

However, he admitted the “sheer weight” of QPR fans trying to get onto the pitch meant officers were unable to hold them back.

He said: “The positive thing about Watford is the safety of the game has improved significantly. There was no intelligence from Saturday there would be any pre-planned disorder. What we did get was intelligence about a pitch incursion.”

Four police horses were brought in from the City of London as back-up in the event of a pitch invasion, which was put in place when up to fans joined players and club staff on the turf.

Ch Insp Harbon said there were 70 officers at Vicarage Road, more than had been present for the Leeds match earlier in the season.

“We had more officers at this match because of the potential for a pitch incursion.

“In the first half there were 16 people ejected from the Rookery. That was really positive stewarding. Some season ticket holders pointed out people clearly not Watford fans. Everything was really peaceful.

“On one occasion, a QPR fan, when they scored, he started jumping up and down. The Watford fans were really quite understanding to start off with but when he wouldn’t sit down, then it started to kick off a bit. He was taken out and arrested and it calmed down.”

Ch Insp Harbon said ticketing issues were a “club concern” but admitted he was concerned by the number of away supporters sitting around the stadium.

Five people were arrested during the match and CCTV will now be studied to identify those fans on the pitch, who could face prosecution.

“We’re going to do a proper debrief with the club for lessons learned,” he said. “It’s a concern. There was no violence. It was just celebrations and it was just the weight of numbers. In the end, the police line broke.

“We need to send out a message that it’s not acceptable, whether celebratory or from a disorder point-of-view. The Watford fans got really upset about it. If I had double the number of officers at that game, we would have still struggled to keep fans off the pitch due to the weight of numbers.”

Ch Insp Harbon added that he would speak to Watford to discuss the involvement of the QPR manager, players and staff in sparking the pitch invasion, which could lead to them being reported to the Football Association (FA).

“The circumstances were not assisted by the management and players and we cannot ignore that,” he said.

“Watford has had a fantastic season. They were unlucky not to get into the play-offs. I’m disappointed we managed to get away fans in the home end and lessons must be learned about that but overall, it’s been a fantastic season. I wouldn’t like this to marr the whole season.”

Watford manager Malky Mackay said his team went into the dressing room at the final whistle so he didn’t see the away fans running onto the pitch.

Asked whether home and away fans should be more stringently segregated, he said: “It was a one-off occasion because QPR had the chance to win the title. It’s not something that comes up often at Vicarage Road.”

A Watford statement released on Sunday apologised to supporters and assured them they were taking complaints very seriously.

A ticketing review will now take place ahead of next season, which will look at the “tolerance” policy applied to away supporters in the Rous and limitations on tickets bought by Watford fans.

The club also set out several “facts” regarding ticketing for the match. It stated that only Watford supporters with a “regular ticket-buying history” were able to purchase tickets; no additional tickets were made available to QPR fans, meaning any sitting among home seats would have had their ticket bought by a Watford fan; and said it had evidence of Watford season ticket holders re-selling tickets to QPR supporters.

Watford also explained that given the number of QPR fans in the Lower Rous, it was decided at half-time to “corral” them together.

The statement added: “A minority of QPR fans entered the field of play after the final whistle, most of which simply to share their joy at promotion with their manager and players - much as Hornets' fans did at Fulham in May 1998, for example.

“And while this behaviour in itself is an arrestable offence, a fact spelled out clearly over the PA system before full-time, some went past a point at which celebration turned to unreasonable and unwelcome behaviour.

“Watford FC will not hide from its responsibilities and accountabilities arising from yesterday's events, and there will be further communication in due course.”