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Kevin Lloyd, group chief technology officer at Barclays, said the bank's IT development stops in December to ensure systems remain reliable over the festive period.
"We issue a change freeze about two weeks before Christmas in an attempt to eliminate any unknown or unquantified changes going into the systems. Although our 'right first time' record has been excellent, we do not risk destabilisation of the environment over the holiday period," he said.
For operations and emergencies, Barclays has scheduled an on-call rota operating over the entire period with the usual working terms and conditions for unsociable hours, Lloyd said.
Council staff at the London Borough of Brent will be working hard over the festive season. Bernard Diamant, the council's director of corporate services, said, "The place has to stay open, so IT staff will be working normally so that the council can deliver its usual services.
"We will also have people that we can call on in case of emergency - even on Christmas Day."
Stephen Pownall, information services director at glass manufacturer Pilkington, said the Christmas break gives his department an opportunity to carry out tasks that would be difficult with the firm running at full speed.
"Most of our factories close over Christmas. As the users are not at work, it is a prime time to implement new systems. We are taking the opportunity to put SAP in our Polish operations as part of a global roll-out," he said.
"The biggest headache at this time is that you get a lot of people trying to sell you things because it is year-end and they have targets to meet."
Pete Smith, IT manager at satellite communications firm Inmarsat, said the holiday period was a chance to catch up.
"In IT, a happy Christmas is a quiet Christmas. Resources are stretched and everything takes much longer to resolve," he said.
"Most IT projects slow down over this period and there are usually no milestones. It is a good time to catch up on documentation.
"With the budget running from January to December, we are busy trying to renew contracts and make use of any surplus funds as best we can. Also, some security settings expire at the end of each year. We need to be aware of these and ensure we have the ability to reset them."
It will be business as usual for the IT department at market research company Mori until Christmas Eve, said to IT director Ben Booth, but the new year is generally quiet. "We take a well-deserved break, because we are all knackered by then," he said.
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