Brighton & Hove Albion have issued a formal apology to Crystal Palace for the incident that saw excrement smeared over the visitors' dressing room before last Monday's Championship play-off semi-final second leg at the Amex stadium.

It has also emerged that Sussex police are investigating after Brighton made an official complaint.

An angry Ian Holloway told his opposite number Gus Poyet what Palace had found as they shook hands on the touchline after the teams had emerged from the tunnel.

Poyet was apparently so disgusted to learn of the incident that he sent an email to staff demanding that the culprit be found and sacked. He and his coaching team have since been suspended by the club, apparently partly because the hierarchy were annoyed by aspects of Poyet's emailed complaint. It is not suggested that any of the trio were involved in the dressing-room incident.

Brighton, who have confirmed no players were involved, insist security will be tightened at the Amex. In an email sent to season ticket holders, the club's chief executive Paul Barber wrote: "It's clearly been a challenging week for our club: defeat at home to our biggest rivals in a play-off semi-final; the suspension from work and pending investigation of three members of our staff; and the revelation of an unsavoury incident that took place in our visitors' dressing room last Monday.

"I can assure you that we will address each of these challenges as you would expect and want us to: namely, professionally and with as much dignity as possible. We apologised to Crystal Palace as soon as the vandalism in their dressing room was discovered, and again more formally a few days after the match. As a result of what happened, please rest assured we have reviewed our internal procedures to guard against this ever happening again."

Barber declined to comment on the suspension of Poyet, the manager's assistant Mauricio Taricco and the coach Charlie Oatway. Poyet appeared to have questioned the ambition of the club in the wake of the play-off elimination and had expressed a desire to meet the chairman, Tony Bloom, to discuss his future.

Sussex police told the Sun: "We were made aware of excrement found in the Crystal Palace dressing room. The club has made an official complaint and police are now investigating."