Advice needed on investing vs savings / mortgage

[Audax]

With regard to over-paying, is it better to overpay each month or to save for 12 months and then whack over a lump sum? Personally speaking I'm leaning towards over paying each month because doing that would mean the money is then out of my account and thus unavailable for me to dip into.

We've always tried to get to our maximum yearly allowance as early as we can, and then save towards the next years allowance once we've filled up the current year. The sooner you get the money into the mortgage, the more beneficial it is.