“Declan is a player with fantastic ability and a proven record at both club and international levels. The process of this transfer has been a big team effort with a clear plan, and we are so happy that Declan is joining us,” Arsenal’s Sporting Director Edu said.

“Declan is a high-quality, young international player who will add great strength to our squad, fitting so well into our strategy of competing with young talented players at the centre of our club.

“It’s great that Declan will be joining up with Mikel, our coaches and his new teammates in good time ahead of the new season.”

Manager Mikel Arteta added: “We’re really happy that Declan is joining us. He is a player with tremendous ability, who has been performing at a high level in the Premier League and for England for a number of seasons now. Declan is bringing undoubted quality to the club and he is an exceptional talent who has the potential to be very successful here.

“Declan has great experience in the Premier League at only 24 years old. He has captained a very good West Ham team and as we all saw, he recently lifted a European trophy. The responsibility and role he has taken on has been very impressive and we are really excited that he is joining us.”