Northern Ireland's police chief has delivered a stark message to the British government on stalled proposals to deal with the legacy of the Troubles - "stop prevaricating and get on with it".

George Hamilton told reporters he was growing increasingly frustrated that three years on from a political deal on a series of mechanisms to address unresolved conflict cases, the plan is not "one further inch forward".

He said if local parties were unable to overcome the impasse blocking implementation of the Stormont House Agreement, then London needed to step up and deliver.

Mr Hamilton said the delays were exacerbating the hurt of victims and leaving police to "soak up" issues that should be dealt with through the new mechanisms.

The Police Service of Northern Ireland's top officer said this was taking a heavy toll on his service, both in terms of costs and public confidence.The chief constable said he felt in an "impossible" situation.

Mr Hamilton said: "Three years has come and gone and they are actually not one further inch forward, they are still waiting to finalise the deal and to do consultations and all the rest of it - I've been getting told that for three years now. The whole thing is borne out of a sense of 'can you just get on with this please'." 

He added: "... if Sinn Féin and the DUP and the political parties here can't get to a consensus to drive it forward in a devolved space, then London need to just get on with it."

The Stormont House proposals, including a new independent investigatory unit, a truth recovery body and an oral archive, are on ice due to a small number of outstanding disputes.

Amid the political impasse on setting up the new structures, Northern Ireland Secretary James Brokenshire has proposed conducting a consultation exercise to establish the wider public's view - but that has yet to materialise.

Mr Hamilton said he had the utmost sympathy for all relatives bereaved in the Troubles.

"For three years now it's been 'wait and see, we're trying, we're nudging, we're close to agreement' - well, actually, all the time of this prevarication the people who are being most disadvantaged is, first of all, the families, who aren't getting the answers," he said.

"Their frustrations and their grief and their hurt is being exacerbated and the cost of all of that negative feeling is being borne by the police, both in financial terms, but more importantly in terms of confidence of those elements of the community who have that frustration, that grief and that anger."

Mr Hamilton's robust remarks came after he wrote an open letter to elected representatives stressing the need for progress.

The police chief was prompted to write the letter after facing intense criticism from families bereaved by the Ulster Volunteer Force's notorious Glenanne gang.

They had urged him not to appeal against a High Court decision that had compelled the PSNI to complete a thematic investigation into the murderous activities of a gang that counted rogue members of the security forces among its members.

Confirming his intent to appeal, Mr Hamilton said the Glenanne case highlighted his difficulties - noting that he was being told he was legally obliged to conduct a probe yet was also being warned his service was not independent enough to do so.