[cynic mode]
Of course, by announcing a price increase on their 1mb tier this month, and then later announcing an increase in speed to 1.5mb (but without the price rising further), they will be able legitimately to claim that they are increasing the speed of the service without increasing the price.
[/cynic mode]
That said, at £34.99, 1mb was costing 3.4p per kbit - at £37.99, 1.5mb would cost 2.5p per kbit, which is considerably better value.