Natwest Mortgage - What a Con

I recently took out an Offset Mortgage arrangement with Natwest, and this month see's my first payment, but boy have I discovered a complete scam which I am going to take up with the Financial Ombudsman, it works like this.

• Lets say my mortgage is £100k
• Each month Natwest adds to my account the interest due on that Mortgage, this is the 24th in my case, so on the 24th they add on £700 in interest, making the total I owe them £100,700
• My payment for the interest goes out on the 1st of each money, so on the 1st, £700 goes into my mortgage account to net off the £700 interest.
• All seems fine, but actually it isn't, because even though interest is applied to my account once a month, it is actually calculated daily, so for 7 days they calculate interest on £100,700... making my interest payments higher

This may not seem much, but work out how much extra interest I will pay on £700 for each month of my 25 year mortgage, it is significant, imagine how much extra you would pay also if your interest is applied on the 2nd of the month and you pay on the 1st, you will have 1 extra months interest to pay.

When I challenged Natwest about this, they simply said, yes... that is what happens, its not up to them to point this out, of course, I have now changed my payment date to the 24th to net off this interest, but this means I have to pay my mortgage twice this month which I am not happy about, I am also claiming back my extra interest I have paid this month. I would of thought a bank would have better scruples.