Why don't old tower blocks in the UK have sprinkler systems to combat fires?

Sprinkler systems are an effective method of fire prevention, particularly in large buildings where access for fire services may be difficult.

But as was the case in the doomed Grenfell Tower, many high-rises across the UK don't have a sprinkler system. Why?

Regulations in England mean that any tower blocks that are higher than 30m (Grenfell Tower is 70m) must have a sprinkler system.

But this only applies to buildings constructed after 2007. Grenfell was built in 1974, and the law was not applied retroactively

If an existing high-rise has major changes, for example to its structure, then sprinklers must be added if they don't already have them. Grenfell Tower had a major renovation costing £8.6m in 2016, but this didn't affect the structure.

Currently just 1% of council tower blocks have sprinklers, and this could be down to cost. Estimates from the British Automatic Fire Sprinkler Association suggest that to fit them at Grenfell would have cost £200,000, a small amount compared to £8.6m renovations that took place a year ago.

These costs can vary for every building, factoring in the size of a building, age and the materials it is built from.

Two firefighters were killed at Shirley Towers in Southampton, when a fire spread through part of the block in 2010. The local council fitted sprinklers to three tower blocks after this at a cost of £1m.

Sir Ken Knight authored a report on the Lakanal House fire, in which he said that while there was significant evidence of the effectiveness of systems such as sprinklers controlling fire spread in buildings, it was not considered "practical or economically viable" to enforce the retroactive fitting of fire suppression systems to all current high-rise residential buildings.

It has also been noted that if the fire spread from the outside, then the effect that sprinklers may have had could have been minimal.

A spokesman for Chief Fire Officers Association in 2015 said that no one had died in a building with a "properly installed sprinkler system working the way it's meant to."