To what extent has the role of Cabinet Ministers declined in recent years?

Cabinet Ministers are heads of government departments, an example would be the Minister for Education. These ministers meet around once a week in the Cabinet, held at 10 Downing Street and the Prime Minister chairs the meetings of Cabinet.Recently it has been argued that the role of these ministers have seen a decline. This is evidenced in the 'sofa government' of Tony Blair, in which he tended to bypass Cabinet in favour of meeting one-to-one with Ministers. Such an example of this is when Blair decided to approve the building of the Millennium Dome without the consent of the Cabinet Ministers, who heard of the decision via the newspapers. However, the strength of Cabinet in the decision making process of government always has varied between Prime Ministers. In the case of the Coalition government, Cabinet was far stronger than under Blair because the government was dependent on Cabinet to pass through its laws in Parliament and present a strong union, whereas Blair had a large majority within Parliament so did not need Cabinet to the same extent. Therefore, I would argue that the role of Cabinet Ministers is not in overall decline, rather it ebbs and flows between Prime Ministers depending on how reliant the PM is for their support.