Plans for a landmark 600ft seafront observation platform have won vital backing from a powerful Government conservation agency.

English Heritage has come out in support of the proposed £20 million i360 tower at the land end of the derelict West Pier in Brighton.

The planning application for the tower will be heard in October and would have stood little chance of success without approval from English Heritage.

The group's reluctance to support Frank Gehry's King Alfred redevelopment scheme along the seafront in Hove has been a serious setback, leading to the planning application being redrafted.

Geoff Lockwood, of the West Pier Trust, which is behind the i360 application, said: "This is certainly a massive and necessary hurdle.

"Without English Heritage support there would have been problems getting this through planning. It's far from a fait accompli but the planning committee has to take note of English Heritage as a statutory consultee.

"They were obviously happy with the scope and scale of the proposals."

In a letter to Brighton and Hove City Council, English Heritage inspector of historic buildings Richard Morrice said: "English Heritage welcomes a project which would provide an outstanding feature on the seafront and a worthy companion to any successor to the West Pier, whether rebuilt or replaced.

"It would achieve an outcome not unlike the original promenade pier by allowing viewing of the whole of Brighton seafront not from seaward but from above.

"Although English Heritage looks with considerable regret on the recent history of the West Pier, we consider the current proposal would prove a fine addition to the seafront. We therefore welcome this application and strongly support the granting of planning permission."

English Heritage has a long history with the West Pier site. Most recently it has been consulting with the trust on the best way to dismantle and remove the wrecked remains.

In 2004 it was heavily criticised for withdrawing backing for a scheme to redevelop the pier, which subsequently collapsed.

Dr Lockwood said he had been overwhelmed with the level of support the i360 had attracted.

It has been devised by architects David Marks and Julia Barfield, who designed the London Eye.

Dr Lockwood said: "It has been remarkable. Of course there are some concerns but I have not encountered any significant opposition.

"It has clearly caught the public imagination. The most common reaction has been stunned admiration."

The plan was featured on Channel 4's Richard and Judy show earlier this week and was warmly praised by the presenters. It is hoped revenue from the attraction, expected to carry more than 500,000 visitors a year, will be used to tidy up the derelict 140-year-old pier.

Public consultation for the planning application finished last week.

Brighton and Hove City Council received 66 letters of objection and 78 letters of support.

A council spokeswoman said: "The recommendation as to whether the scheme should be granted or refused will be primarily based on the extent to which the planning application accords with Brighton and Hove's development plan policies.

"It's not a referendum based on how many letters we have in."

The application seeks permission for the partial demolition of the Grade Ilisted pier structure, construction of the spire, a heritage centre, shops at lower promenade level and a coach park.