Manifesto commitments are important. How else is the voter supposed to gauge the ideological direction of a political party? What is often wrong in this country is the tribal nature of politics; All too often people will vote based around a partisan gut feeling, rather than what the manifesto commitments of a political party might mean for them and the country.
And consequently a manifesto pledge provides a useful benchmark for measuring the depth of a governments commitment to its ideological values. Chopping and changing manifesto policy on the hoof, reacting purely to populist desire or media criticism should not be desired, since it represents an abandonment of considered principles ( manifesto commitments) in favour of the purely popular vote - power at any cost.
So it becomes a balancing act; Of course a government must be alert to fast changing circumstances and be willing to modify legislation or ideology if they fly in the face of prevailing currents, but governments need to be careful about deviating from manifesto pledges; Doing this too often demonstrates pitiful planning and naked populism and risks alienating your core voters; Failure to respond at all to current events and modify manifesto commitments risk being seen as being arrogant or out of touch or hidebound.
But both the media and the public are conditioned to think that a significant deviation from a manifesto commitment ( a u-turn) represents weakness, flipfloppiness, lack of resolve - and this image was enshrined by Maggie Thatcher,very fond of the Iron Lady description with its implications of adamantine resolve, when she made the now rather famous " U turn if you want to - speech".
Where one party rubbishes anothers political suggestion for partisan party political purposes - as the Tory party did when addressing Labours calls for a price freeze from the energy companies - and then effectively appearing to follow exactly the same path themselves shortly after when it became apparent that the original idea was hugely popular to the electorate- could rightly be termed a U-turn, could rightly be considered both hypocritical and cynical, and so opens the Government and the Tories up to those charges.
That's not Tory- bashing for the sake of it, that's a fair assessment of the current situation regarding cost of living issues and energy prices right now. It's just the political reality. Interesting to note that the Government are now denying that such an approach has been made at all :)