Mortgage Float Down: L&C broker

[areaboy]

Morning all, I had a mortgage offer at 5.5% from Halifax a month ago brokered through L&C. I can see now that the same product interest has gone down a bit, and there are other products out there that would be cheaper. I recall my broker mentioning something about being able to change to a better rate if one appeared before I'd actually bought the house. Is this sort of thing possible, if so, how does it work? Thanks!