Ivan Toney's equaliser for Brentford saw league leaders Arsenal drop two points in the title race but replays showed it should have been ruled out for offside in the build-up, leading Mikel Arteta to accuse officials of "changing the rules".

Arteta felt it should have been disallowed because Ethan Pinnock appeared to be offside while blocking defender Gabriel Magalhaes as a free kick was delivered into the area for Toney to volley back across goal.

Across London, Brighton & Hove Albion saw their quest for European football hit a speed bump at Crystal Palace when they were held to a 1-1 draw but Pervis Estupinan's goal was wrongly chalked off for offside.

However, the offside line on replays was wrongly drawn for James Tomkins instead of fellow Palace defender Marc Guehi, who was behind him.

"PGMOL can confirm its Chief Refereeing Officer Howard Webb has contacted both Arsenal and Brighton & Hove Albion to acknowledge and explain the significant errors in the VAR process in their respective Premier League fixtures on Saturday," it said on Sunday.

"Both incidents, which were due to human error and related to the analysis of offside situations, are being thoroughly reviewed by PGMOL."

Webb, a former Premier League referee, became the Chief Refereeing Officer at the PGMOL this season.

Prior to the role he was with Major League Soccer's Professional Referee Organisation (PRO) in 2017 as their manager of Video Assistant Referee operations before taking up the role of general manager of PRO.