To see video footage of Ian Oakley's selection as the Tory partliamentary candidate: click here

A comprehensive inquiry into the Watford Conservative Party must be launched to discover how Ian Oakley was able to sustain his three-year campaign of hate, Liberal Democrats have said.

The party has, both nationally and locally, called for Conservative leader David Cameron to investigate the town’s Tories and find out how Oakley was able to continue his sick programme of attacks.

On Tuesday, the 31-year-old parliamentary hopeful pleaded guilty to 75 separate cases of harassment, criminal damage and intimidation, directed towards his political rivals and Liberal Democrat supporters.

The true horror of his prolonged harassment of election rival, Sal Brinton, was also revealed in St Albans Magistrates Court.

The court heard Oakley had sent pornographic images to his rivals’ homes, distributed poison-pen letters branding two Lib Dems paedophiles and painted obscenities on dozens of cars and homes.

Following the revelations, local and national politicians have questioned how Oakley was able to win selection in 2006 and how his vile campaign went unnoticed for so long.

Oakley was elected by an innovative, open primary system in November 2006.

Liberal Democrat MP, Ed Davey has already written to Mr Cameron demanding a full inquiry to “ensure such an appalling course of events is never repeated”.

The Conservative Central Office said yesterday it would not launch any investigation until Oakley had been sentenced.

Mayor of Watford, Dorothy Thornhill, said she was “disgusted” by the national party’s attempt to wash its hands of its former candidate.

She said: “I am just quite simply relieved it is all over and we can get back to business as usual.

“But I am shocked we have had no formal apology and I am disgusted by the way the national Conservative Party has distanced itself from the situation.”

Oakley’s sensational admissions have also called into question the legitimacy of three election results in Watford.

In 2006, Conservative councillor Zoe McQuire was elected to the council seat in Park ward by just three votes.

The following year, in the Leggatts ward, Amanda Grimston was returned by the margin of two votes.

And at this years’ election in Nascot, Conservative leader Andrew Mortimer was re-elected by 47 votes.

It emerged in court that in the build-up to that election Russell Willson, Councillor Mortimer’s main rival had been the target of Ian Oakley’s harassment.

While nobody is suggesting any of the councillors were part of Oakley’s plans, Councillor Steve Rackett, of the Green Party, says the trio could have been the unwitting benefactors of his actions.

He has called for by-elections to be held in all three seats.

Councillor Rackett said: “Clearly campaign workers and party activists can not function as well when they are being subjected to intimidation and harassment. It calls into question the legitimacy of the results and the legitimacy of their mandates.”

Councillor Rackett said he had already written to the central Conservative headquarters demanding it suspend the local Conservative party.