The 23-year-old non-contract striker, who has netted 14 goals for the Pilgrims so far this season, has agreed terms with United’s county rivals after Trinity submitted an official seven-day approach for his services last week.
United boss Graham Drury was massively disappointed to lose his striker, but admitted Jones had received an ‘unbelievable offer’ from the Blues — on a contract until the end of the 2013-2014 season.
Drury told bufc.co.uk: “We desperately wanted to keep Mark and in fact offered him more money to stay, but we were unable to compete with what was an unbelievable offer from Gainsborough.
“We support the lad with the decision he has made, which is understandable given the fact he is not working away from football at the moment.”
Jones’ 14 goals arrived in 29 appearances for the Pilgrims — that last of which was the winner against Colwyn Bay last week.