Lump sum off mortgage - penalty decreased since last week

[dubinamerica]

Considering paying a lump sum off of our mortgage. I rang up last Friday to get a quote for the penalty and have just done the same, the penalty ( or break fund fee) has decreased slightly over the week. The loan amount and term are the same, so the underlying rate must have increased (so the difference decreased)..

Anyone any thoughts on whether this underlying inter-bank lending rate is on the way up as it's getting harder to lend between banks? Or anyone know where I can check that rate on a daily basis?