It is the largest-ever closure plan by the company and will radically change the face of the bank, according to Unite.
Thousands Without Power After Storm
Thousands of homes are still without power after gales and lightning strikes caused by a so-called ''weather bomb'' swept the north of the country.
Around 27,000 properties in the Western Isles and Skye have no electricity due to the stormy conditions along the west coast of Scotland.
The process behind the storm - rapid cyclogenesis - is known colloquially as a "weather bomb''.
Weather warnings remain in place for much of the UK but the mainland has so far survived relatively unscathed, with the northern isles around Scotland worst affected.
Hundreds of engineers worked yesterday and through the night to restore power to more than 30,000 homes across the Western Isles, Shetland, Orkney and rural areas on the west coast but further lightning strikes caused additional disruption.
SSE said lightning had been the biggest feature of the "weather bomb'', with more forecast for today.
A spokesman said: "Just after 9am this morning a lightning strike near Fort Augustus resulted in a loss of supply to Skye and the Western Isles. In total around 27,000 customers are currently without power.
"Engineers are now working on the fault and we are hopeful that supplies will be restored within three hours.
"We'd like to apologise to customers for the loss of supply this morning. We appreciate that many of these customers also lost supply yesterday and we'd like to assure them that we are doing everything we can to get them back on as quickly as possible.
"We have good levels of resource on the ground across the Highlands and Islands and will work hard to ensure that all faults are repaired as quickly as possible.''
There has also been disruption to travel across Scotland with some coastal roads flooded, and ferries and trains cancelled.
A wind speed of 144mph was recorded on the remote St Kilda islands, with gusts of more than 80mph also hitting some low-lying areas.
A Met Office amber - "be prepared'' - warning had been in place throughout yesterday for the west coast of Scotland, the Highlands and Islands, Orkney, Shetland and Northern Ireland.
This was downgraded to a yellow - "be aware'' - warning as the gales gradually eased to be replaced by wintry showers bringing snow and ice to the country.
Forecasters said there could be some "significant'' snow accumulations in parts of Scotland with the rest of the UK set to see the white stuff over the weekend.
There is an 80% probability of icy conditions and some snow in the North of England between midnight on Friday and Sunday morning, according to the Met Office.
A cold weather alert has been issued and a statement said: "This weather could increase the health risks to vulnerable patients and disrupt the delivery of services.
"The recent cold and unsettled weather is expected to continue through to the coming weekend. A band of rain, and hill snow in the north, is expected during Thursday night. There is also a risk of some snow down to lower levels at times in eastern and north-eastern parts.
"Rain and snow will clear early on Friday, leaving bright but cold conditions. Brisk winds will exacerbate the cold feel at times. A few wintry showers will follow but any snow accumulations will be mainly restricted to hills.''
During the worst of yesterday's weather, a fishing vessel had to be escorted to safety off Orkney after it was hit by a wave which smashed windows on the bridge.
The British-registered vessel O Genita, which has a Spanish crew, was escorted to Westray in Orkney by an RNLI lifeboat. None of the 16 crew were injured.
Scotland's Deputy First Minister John Swinney last night praised frontline staff for how they dealt with disruption to travel and power supplies.
He said: "Obviously there has been transport disruption, principally on the ferry network and also on some of the coastal rail services where it's just been unsafe to run trains because of the dangers of the coastal flooding that could have taken place.
"Some alerts remain in place, and we are not out of the woods yet, but any necessary repairs and safety checks on the transport network are expected to go ahead as planned.''
Network Rail and ScotRail expect full services to be running throughout today.
The SNP claims a "Hard Brexit" will cost 80,000 jobs in Scotland.
A bullet has been recovered from a tree where a man was shot near a primary school.
Scotland's jobless total rose by 11,000 in the three months to November.
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