Crimes committed under the influence of drugs and alcohol should carry tougher sentences, a Commons committee has recommended.

The call came as the home affairs select committee published its review of plans put forward by the independent Sentencing Guidelines Council (SGC).

According to the MPs, the SGC should toughen up its latest draft guidelines on the seriousness of crimes.

They said that "being under the influence of drugs or alcohol" should become an aggravating factor when assessing an offender's culpability and length of sentence.

"Although hard evidence is hard to come by, the committee was concerned that being under the influence of drugs or alcohol is sometimes used by defendants as an excuse for their behaviour," said chairman John Denham.

"The committee believes that these arguments should be rejected by sentencers and that being under their influence should instead be an aggravating factor."

Murder pleas

The MPs also called for tighter rules on guilty pleas in murder cases.

Reductions in sentence for guilty pleas in murder cases should not normally be granted in addition to reductions for other mitigating circumstances, they said.

"When the draft guidance was published the proposed reduction of sentence for a guilty plea attracted a great deal of controversy," said Denham.

"The committee believes that parliament wishes murder to be treated as significantly different to other offences.

"We do not believe that the current draft guidance fully reflects the wishes of parliament or public disquiet about the reductions for a guilty plea.

"That is why we want to see sentencers advised that in the case of murder, reduction in sentence for a guilty plea should not normally be granted in addition to reductions for other mitigating circumstances."

Lack of scrutiny

The MPs also expressed concern about the way the legislation setting out the framework for the changes was scrutinised by parliament.

Responding to the report, shadow home secretary David Davis said the provisions for murder tariffs were introduced "without proper scrutiny".

"There is genuine concern about potential reductions in murder sentences - such action sends out the wrong signals to violent criminals and completely undermines the government’s claim to be tough on crime," he said.

"Sentencing should be determined by the crime, not by prison capacity."