In Cameron's 2010 “Contract between the Conservative Party and you” he wrote,
“If you elect a Conservative government on 6 May, we will:
1. ...
2. ...
3. ...
4. ...
5. Control immigration, reducing it to the levels of the 1990s – meaning tens of thousands a year instead of the hundreds of thousands a year under Labour.”
There is a difference between "will" and "shall" which express either an obligation or an intention depending on to whom or what it refers and it crops up in disputes as to the intended meanings in contracts.
"I, we (first person) … will (OBLIGATION) … shall (FUTURE INTENTION)
You, he, she, it, they, the Party (second or third person) … will (FUTURE INTENTION) … shall (OBLIGATION)" [emphasis added]
As Cameron used, "we will", that was an obligation.
If it was claimed the Labour Party would win the election, that was a future intention.