Slideshow: St Mary's is given a makeover

From 170ft up, the cars driving past St Mary's Church look like children's toys and there's not a sound to be heard from the busy road.

But it's far from quiet at the top of the church's tower as the hustle and bustle of everyday life going on below has been replaced by a much eerier sound.

Up among the church's pinnacles and stone angels, all you can hear is the howl and whistle of the wind as it blows through protective nets, making the scaffold floorboards creak.

It's cold, wet and mind-blowingly high, but the busy team of stonemasons working on the tower's repair don't seem to mind.

On a clear day they can see Chichester Cathedral in the distance and Portsmouth sprawled out at their feet.

But on a day like today, when there's not much more than rain clouds and grey drizzle on the horizon and the wind speed has reached 39mph, it's a different picture.

Fortunately, they're shielded from much of the wind and rain by the netting draped around the structure, but that also means it's impossible to see them from the ground.

As the rest of the city gets on with its business, people are oblivious to the stonemasons working away on one of the tower's 27 scaffold levels.

View a slideshow of their work.

Throughout the cold winter months a team of between eight and 10 of them have been up there at any one time. Pollution and the salty sea air have taken their toll on the stone work on the tower's 24 windows, making conservation work now vital.

Each window has to be meticulously measured and mapped out on giant sheets of orange plastic before any stone can be cut away.

The templates are then cut up and the measurements sent off to the Doulting quarry in the Mendip Hills, Somerset, in order for the new stones to be hewn out.

Each new stone is then sent back to Portsmouth and carefully fitted into place.

The existing mullions – the structural vertical pieces of stone work that separate the window panes – can only be cut away when the new section is ready to be fitted, but other parts of the stone work can be chipped away in advance.

It's a time-consuming job and each window throws up its own challenges, as the modern-day stonemasons figure out how best to conserve and preserve the intricate archways, or tranceries.

'Every window is substantially different,' says project manager David Collier, from St Blaise, the company hired to carry out the work.

'When you're working on a building like this, part of the fun is working out how it was built.'

Conservators use syringes filled with grout to fill in holes that have appeared over the years, before repointing work with mortar is carried out.

Access is via a hoist cage running up and down the side of the building or, if the wind speed is too high, on ladders and platforms running the length of the scaffolding. 'I'd suppose you could call it a labour of love,' laughs David.

'The guys are dedicated and it's great to work on all these buildings that could last for the next 800 years. It gives you a real buzz.

'The stonemasons are proud of their work. There can be a windchill factor of -15C up there and they still love what they do.'