A new project, which may prove to be a very considerable task, has been added to the conservation programme – the window of the South West Transept.

This Great South Window, one of the largest in the Cathedral and dating from the early 15th Century, with 12th Century glass, was repaired during the 1970s. You may remember the stonework at the apex of the Transept being replaced. A number of new heads and pinnacles were carved at the same time and the glass was cleaned.

At the beginning of July, a piece of masonry from one of the stone mullions fell out, alerting the Cathedral to a major problem. On close inspection, stone from at least one other mullion was found to be in danger of failing. The possible cause is that the expansion and contraction of the metal transom bars in the very hot spells of weather in recent summers, and particularly in late June this year, has split some of the stonework, affecting the overall strength of the window.

The first priority was the safety of visitors and staff, and so the South West Transept was immediately closed off inside and out, and protective scaffolding put up to catch any further falls of stone. Scaffolding is now to be erected both inside and outside the window.

The two sections will be braced through the window openings to support the stone tracery. All the stained glass, some of the earliest – and finest – in the Cathedral, including the 12th Century series of the ancestors of Christ, will be carefully taken out and safely stored.

The scale of the challenge, exactly what needs to be done, and the costs will become much clearer during September and October. This is now the priority project for our craftsmen and women.