Website: http://www.openplan.co.uk/Mortgage/default.asp
Phone: 0845 070 5090
The Woolwich mortgage was the first to offer offsetting and flexibility, but they're not alone now, and a complicated fee structure, small range and messy site make this a less than pleasant experience.
The Woolwich pretty much invented flexible mortgages (they call it "Open Plan"), and also invented offsetting; where your earned interest on savings can offset your mortgage payments. Their Offset Flexible products form the basis of the Woolwich mortgage service, all you need to do then is decide which other benefits you'd like bolted on. You can choose a fixed rate, discounted rate, tracker or cashback, depending on your circumstances and some fairly stringent lending guidelines. Some products are only available to existing Woolwich (and Barclays) borrowers.
The fees, clearly laid out on- site, are fairly substantial - £195 and up for a valuation, £25 penalty if you get your insurance elsewhere etc.; although some of these "extras" are waived on some products. That said, the trend these days is to removing these complications, and the Woolwich mortgage is behind the times in this respect.
The site is not easy to use, and comparisons of products are hard to make- if you're already a Woolwich accountholder, this might be an easy choice; otherwise get some other quotes and certainly do your learning elsewhere.