The 19 year old will join fellow United youngster, Bobby-Joe Talyor, who has recently extended his stay at Rowley Park.
Liam will be in FA Cup action today, as the Saints take on Wroxham in the first qualifying round.
U's Director of Football, Jez George, said:
"St Neots are a really good club and have looked after Bobby-Joe really well since he has been there. We speak regularly to Ian Parr and also get footage of every game, which helps us to monitor and assess the performances and progress of our players. We are pleased to have developed an excellent working relationship with St Neots Town which can grow to benefit both clubs in the future."