The developer behind proposals to upgrade a Birmingham office which came under fire from city councillors said the plans were a crucial part of the city’s quest to attract inward investment.

Developer Abstract Land wants to add an extra floor and modernise the rooftop of the 19th century Grade II-listed 55 Colmore Row – the home of Wragge and Co – as well as renovate the building’s old banking hall and develop its Barwick Street frontage.

Birmingham City Council’s planning committee has deferred the scheme, having been critical of the plans, but Abstract boss James Howarth is confident approval can still be secured.

Mr Howarth said: “We have to bear in mind that the planning process sees lots of energy in the first 12 months before it comes to the committee and then they can either approve, defer or reject an application.

"As the decision on our application was deferred at committee, the design team is working with the council and awaiting guidance on the provision of additional information.

“This is a process that has been carefully researched and planned, creating a body of evidence with the local authority which has received the resounding support of the planning officer.

‘‘Clearly there has been a lack of understanding about aspects of the plan. What’s important is that we get a balance between what’s there now and what can be achieved,’’ Mr Howarth said.

‘‘Everybody can have opinions but they must have opinions on what’s the right thing to do rather than just what it looks like and sometimes you don’t get the feedback that’s necessary.

‘‘At the end of the day, we want to secure the best occupier for arguably the city’s best address.”

Committee members were scathing of the rooftop plans, which they claimed would ruin views of the Colmore Row Conservation Area.

Coun Barry Henley (Lab, Brandwood) said: “Development should preserve and enhance a conservation area, and this fails that test.

“This modern glass lump destroys the elegance of the facade and mocks other buildings in the conservation area. It looks like a UFO has landed on the roof. Agreeing to this would be a travesty,” he said.

Coun Henley was also scathing of the proposal to replace the 1990s red brick extension on Barwick Street with a “glass curtain”.

“It is a modernist monstrosity,” he added.

Only two of 11 committee members supported the design.

Coun Bob Beauchamp (Cons, Erdington) said: “I am quite impressed. I find the rooftop modern and sympathetic.”

Birmingham’s conservation and heritage panel and English Heritage had both objected to the rooftop part of the development.

However, Mr Howarth said it was important to clarify that the application was to add one new floor to the building, not two and that the building was 19th century – built around 1870 – rather than 18th century as previously reported.

He added that unlike the nearby Grand – which is currently being assessed for a potential complete renovation which could see the historic hotel brought back to its original use – just the facade and the banking hall remain from the original building, the rest of which was demolished and rebuilt in the 1980s.

He said there was “nothing genuine” about the rooftop, which was made of fiberglass, and that the new design would lend a new “integrity” to the roof and enhance the facade.

He said it was important the city embraced projects like that proposed for 55 Colmore Row if it was going to reach its aspirations.

He said: “We want to see institutional investors looking positively at Birmingham where people like us come up with ideas and they are supported by the local authority, which we have been.

‘‘We don’t want a message that Birmingham is closed for business.”

Wragge and Co is set to move into its new home at nearby Two Snowhill in 2013.