The Liberal Democrats have abandoned leftwing voters who could not bring themselves to back Labour, and will instead present themselves at the next election as a party that has moderated the Conservatives, according to the attorney general, Dominic Grieve.

He also predicted the government was about to become "the least populist seen in many a year. There is a real danger that this government will not be populist enough."

In a wide-ranging set of remarks to the thinktank Politeia, Grieve also admitted:

• there had been "a spontaneous combustion" generated from the internet against the sale of forestry commission land.

• the government could yet decide to undo its connection with the European Convention on Human Rights.

• the English Defence League's anger at what it regards as "appeasement to Islammist extremism is something politicians may ignore at their peril".

• the increasing populism of newspapers, desperate to maintain circulation, is becoming a problem for government.

Grieve openly expressed his concern that the government's efforts to be popular are being hampered by the need to keep the coalition together. He said: "The coalition government is hamstrung from being too populist because of the internal contradictions within it. You are about to experience, or are experiencing, what I suspect is going to be the least populist period of government that you have had for many a year.

"The Liberal Democrats are suffering in populist terms at the moment, hugely weakened by the fact that they have decided to get rid of, or be willing to shed, the support of people who are on the leftwing of the spectrum of politics but couldn't bring themselves to vote Labour. They have effectively abandoned them."

He said Liberal Democrats had openly discarded these voters "on the basis of the belief that over a five-year period they will be able to demonstrate that they have acted as a moderating force to Conservative populism and thereby get the plaudits of the electorate in five years' time by showing what moderation and sound political judgment can deliver in terms of benefits to the electorate. It will remain to be seen whether this remarkable experiment, which shows some courage on their part, will in fact deliver the outcome which they want."

He added: "Conservative members of the coalition are in reality equally circumscribed in certain areas about pursuing some of the agendas which might be popular and appeal to their electorate. It will be an interesting challenge whether that lasts or not."

Grieve – in the past a supporter of a British bill of rights – also opened up the possibility of the UK withdrawing from the European Court of Human Rights.

He said: "The court doesn't have the last word. It only has the last word so far as parliament has decided that it should. We could, if we wanted to, undo that – I think we should always bear that in mind – and actually undo it without some of the consequences we have over the European Union."

Reflecting on last week's Commons vote opposing giving prisoners the right to vote, he said the government now faced a conundrum. "On the one hand, here is a decision by the ECHR which is clearly not liked by the prime minister and virtually everyone else in government I can think of, including myself. And yet here is a convention which has been seen as being a defining benchmark for UK values and standards since the late 1940s."

He admitted that popular opposition to the sale of forests had not been concocted by the media, but was "a spontaneous combustion brought about by the internet, which grew on a momentum of its own. National newspapers jumped on the bandwagon once it started, but actually the bandwagon started without them."