The 6'4 centre-half made 26 appearances in Barnet's Conference National winning side, as well as playing for our neighbours Aldershot Town in Non-League's top flight.
Jack, who now lives in Fleet, turned professional with Southampton in 2009 at the age of 18, after spending four years in Chelsea’s Youth system.
Upon completing the signing, Manager Spencer Day said: “This massive signing has come out of the blue but to get Jack today is a fantastic boost.
“He’s another player that has bought into our policy of signing local, high quality players that have come to enjoy their football in a Club full of positive momentum.
“Jack is good friends with a number of our players and this only bodes well for the season ahead.
“Again I must thank Ian Allinson and St Albans who sanctioned the deal at such short notice. Our Pre-Season business is almost done and we can go into the last eight days of games and training with extra confidence as we look forward to next weeks competitive start.”
Boro's latest recruit added: “Delighted to sign. Great club which has good momentum moving forward! Looking to push for promotion.”