The family of a British hotelier brutally murdered in St Lucia are “relieved” that a full investigation into their son’s death will begin after the Home Secretary authorised British police assistance.

The investigation into the murder of Oliver Gobat was given the green light for assistance from British police after the Home Secretary, Theresa May, addressed a letter to Mr Gobat’s brother, Adam.

Mr Gobat, 38, was born in St Lucia, but grew up in Esher and went to school in Wimbledon.

His body was found in the passenger seat of his Range Rover in the Cap Estate on the north-east tip of the island at about 10pm on April 24, 2014.

He had been shot twice in the head before his body was torched in a car.

Mrs May’s authorisation of assistance was initially delayed because of concerns about St Lucia police after a report by the Caribbean Commonwealth alleged serious abuses of power, including murder and planting of evidence.

Mrs May’s letter said: “It has taken some months to get a full picture of this, but you will be pleased to learn I have now agreed to provide in full the assistance required. However, the provision of assistance is dependent on a number of conditions I will expect to be met by the St Lucians.”

Mr Gobat’s mother, Helen Gobat, said: “We are indeed relieved that at last a full investigation into Oliver’s murder will begin next month with the assistance of the British police. Even though it is 18 months since his assassination, it is never too late.

“There is an amount of information and leads and we feel confident that with professional assistance from an outside force, we will make progress.

“We cannot allow his murder to go unchallenged and never to discover the reasons behind it and the circumstances. Revenge is not uppermost in our hearts, we just want justice.

“Ollie was a man of very high ethics and integrity.”

A spokesman for Surrey Police confirmed that although the authorisation had been given to work with the St Lucian police, no formal request had been made.