Jacob,

Whether it's for your own Principal Private Residence or for a buy to let investment, you can't beat a good broker. They don't all charge a fee either. I have used a broker to obtain 16 BTL mortgages in the space of six months. After a short break from accumulating, I wanted to remortgage our home. We had a Woolwich offset mortgage, and when I saw Woolwich advertise a better product, I asked them if I could move to that product. The answer was no. (It never ceases to amaze me that companies treat brand new customers much better than existing customers, but that's the perverse society we live in).

So I asked my broker to see what he could do. Result - I got offered up to 85% on a Northern Rock mortgage (though I only took 70%) and was able to put about half the loan back immediately into offset. Though total cost of ownership is notoriously difficult to compare between lenders, I reckon over the space of two years, I will have saved over £4,000, and more to the point, I have a huge cash pile of offset mortgage to plunder if I see investments that require cash input.

And just before anyone comments about the lack of liquidity in Northern Rock, I pulled £100K out of offset last month - just to be sure they had money, and it's sitting in a bank account ready to use. I was nervous that they wouldn't advance against the offset, but they did without any issues.