Porterfield had a trial at Bristol in May, after returning from the World Cup - in which he made 172 runs in nine games - but he was not signed up then.

Left-handed opener Porterfield spent a spell as an MCC Young Cricketer at Lord's between 2004 and 2006.

MCC head coach Clive Radley said: "Will has got his rewards for impressing with us, Leeds Bradford UCCE and Ireland."

Porterfield was Ireland's highest-scorer in 10 one-day matches this year, including county cricket's Friends Provident Trophy, with 250 runs at 25.00.