Whilst it's right that quality runs are important you have to be careful. To get the benefit from quality you need to run hard and be fresh for the session. If you do too much you will be tired and will injure yourself and /or not get the full benefit. Most mileage should be at a pace you can recover from. I would say nearer 8 minute miling. Perhaps 10 % quality. As someone said there is a tendency to run slower runs too fast and faster runs too slow.

The best way to do London is to first get a good for age place. You have a different start ( with the celebs!) and can be away quickly.