One of the country's finest parish churches, St Peter Mancroft in Norwich, was given a new lease of life thanks in large measure to the efforts of architect Robert Potter, who has died aged 101.

He undertook a radical roof restoration when there was the gravest risk that the church could have been lost.

Mr Potter was architect for 25 years and worked closely with the then vicar, Canon David Sharp, in transforming the church, founded in 1075 and rebuilt in 1455.

An appeal launched in April 1979 raised more than �400,000 and enabled essential projects, including restoration of the organ, to be completed.

In the early 1960s he led the restoration of the roof, which, unusually, runs the whole length of the building.

Its weight was forcing the walls outwards because wood behind the load-bearing wall-posts had perished.

The lead was stripped and the roof was 'raised.'

As Canon Sharp recalled: 'It was a massive job, and a huge risk to his reputation, but it was successful. This work is recorded on a slate wall plaque just east of the south entrance.

'He has left a major mark on the church, being responsible for the radical roof restoration.'

Born at Guildford in Surrey, Mr Potter studied architecture at The Regent's Street Polytechnic in London and established his own practice at Salisbury in 1935.

After war service with the Royal Engineers in India, he became increasingly in demand in the West Country and further afield, working on Chichester Cathedral in Sussex and the Bodleian Library at Oxford.

He was also surveyor to the fabric of St Paul's Cathedral and was made an OBE in 1993.

Despite the other demands of his practice, he cared deeply about St Peter Mancroft. He supervised the removal of the utility vicarage at the chantry and its replacement with a building to house the Mancroft Advice Project.

Another early task was recladding the intricate lead-covered fleche that tops the tower. Leaks were causing the core, a softwood wrongly used by the Victorians, to rot inside the lead; and two of the 15ft flying buttresses were discovered to be empty leaden shells.

Later, his role was crucial in building the Octagon at Mancroft, especially in delicate negotiations with the heritage and planning authorities.

Designed for smaller, more intimate groups, it became a visible link between church and city; and for two months the whole east end of the church was supported by two huge sleepers while the foundations were strengthened.

The central roof boss in the Octagon – St Peter's keys in relief – was commissioned by him from the carver at St Paul's and was Mr Potter's gift to the project. It is intricately carved from a single piece of wood.

Canon Sharp said: 'Robert Potter was a great architect, imaginative, enthusiastic, and bubbling over with ideas. He was also a very committed Christian himself; his son became ordained.

'It was not just the building that fired Robert's enthusiasm but what it stood for and how it could be used for the Church's mission.

'His achievements at Mancroft brought the building fully into the 20th century, preserving its medieval beauty for us but at the same time facilitating its outreach into the community.'

Mr Potter is survived by his second wife, Margaret, the three children of his first marriage and two stepchildren.