Forest issued an unprecedented statement condemning Attwell's selection after having three penalty appeals turned down.

Forest's fury put the spotlight on the PGMOL, the refereeing group that officiate Premier League matches. So, how does it select officials for games? And what criteria does it take into account?

Before every match round, there is a complex discussion held by chief refereeing officer Howard Webb and other PGMOL officials to decide which officials will be appointed to each match.

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Its selections are based, in part, around "allegiance forms" submitted by all referees and officials, in which they disclose the teams they support, and any others they have connections with.

These forms, submitted at the start of each season, focus strictly on geography and rivalry. So, for example, an official who is a Birmingham City fan should never be allowed to referee Aston Villa.

However, that official would be allowed to officiate a match involving West Bromwich Albion because, while there is a rivalry with Birmingham there, it is not deemed a strict conflict of interest.

It is not explicit that Attwell, whom Forest claim is a Luton fan, cannot officiate games involving other clubs involved in the relegation battle.

That said, practical, common-sense decisions are applied wherever possible to avoid such clashes.

PGMOL has to allocate six match officials to each Premier League match, which means a total of 60 officials are chosen for each Premier League match round.

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It has a pool of around 80 elite officials to select from, although up-and-coming officials are promoted at various times to give opportunities for development, and in order to widen and maintain the pool.

Fourth officials are often selected from the group slightly further down the PGMOL standings, who typically work in the Championship.

The criteria used for weekly selections

This is complex and not an exact science but the criteria used are:

• The teams the officials support. But as mentioned above, this only prevents them from officiating in a match involving a direct rival, not always a rival in terms of the league table.
• Performance. How well did that individual perform in their last game? Officials who make significant mistakes are often rested the following week, or moved to lower-profile games or positions. This is to ensure 'in-form' officials get the most important matches.
• The last time a referee officiated the teams in question. Officials are not allowed to referee the same team for two matches on the trot. PGMOL tries, wherever possible, to ensure a month between games.
• Merit. There is also an element of picking the best person for the job, depending on the importance of the game, but all officials used in the Premier League are from the elite group.
• Championship consideration. The selection process is further complicated by the fact PGMOL also has to select officials for the second tier. If there is a particularly significant game there, for example between promotion or relegation rivals, they may use more of the elite group of officials for that game.

'I never referee Newcastle games'

Michael Oliver, one of the country's leading referees, gave an insight into the selection process in an interview with the Mail on Sunday newspaper in 2021, stating his Newcastle United allegiance prevents him from officiating their games.

"I never referee Newcastle games," said Oliver. "We have to declare if we have an allegiance to any club or if a family member works at a club.

"You can't do any match involving that team and I can't do Sunderland, either, for obvious reasons.

"Because Newcastle [were] invariably involved in a relegation battle, when you get to March or April, it means I can't referee anyone around them towards the bottom three.

"If Newcastle needed a point to survive and the team they were fighting to get above was, say, Villa, I couldn't referee Villa's game either. I wouldn't want to. It's not worth the hassle."