Sometimes the callers they advise are less sweetly reasonable than the staff themselves, breaking into strange oaths when told they have left some crucial point of information at home. Barry Desaleux, the manager of the office's self-assessment team, is unmoved by these outbursts. "Sometimes people get shirty," he shrugs. "But that comes with the territory."
Last Wednesday - 30 September - was the last day for the 9 million taxpayers involved in self-assessment to get their returns in if they wanted to be sure the Inland Revenue would calculate the tax they owe. That makes it one of the busiest days of the year for tax offices.
This is the second year of self-assessment, and Barry is keen to make it clear things have improved since last year's debut of the system. "We didn't get off on the right foot last year, and we didn't start as we would have liked," he says. "This year we've made sure we've got a better handle on returns as they come in. It is 100 per cent better this year."
Barry can afford to observe the whole process with a degree of detachment, as his own tax goes through the far simpler PAYE system.
Upstairs from reception at Woolwich, a group of middle-aged women is opening that morning's post, which contains nearly 400 more returns - about three times the normal daily load.
The most urgent task on deadline day is to get all the forms logged into the system so that there can be no doubt that they arrived in time. This is done by entering each form's 10-digit UTR number into the computer. When the time comes to process the forms, they are handled more or less in the order they arrived. But anyone who envisaged this as a hi-tech operation would be disappointed.
Work at the Woolwich office, which serves about 50,000 taxpayers in south London, seems to depend as much as anything on the staff's own complex system of coloured cardboard notes. Each colour indicates the particular type of return contained in that bundle. The high-priority green cardboard tag, self-assessment team co-manager Alain Ilsley confides, means that a repayment is due.
Entering the UTR numbers first thing on Wednesday is a clerical officer, Vilma Selvaratnam, who tabs in each number by hand. Each form contains the same information in bar-code form but, because Woolwich does not have enough scanners, many forms must be entered by hand instead. No one is using the two scanners available. It is Vilma or nothing.
One of the most common errors people make when filing their returns is simply to forget to sign them. Less than an hour into the day, and Vilma already has a file of 20 or so unsigned returns balanced precariously on top of her computer screen.
The unsigned forms will be returned to the taxpayers involved with a note suggesting they sign them and get them back as soon as possible. Only when the amended form gets back to Woolwich is it registered as having been safely received.
Tax offices will accept not only their own return form, but also those rewritten by large accountancy practices, providing they fit the Inland Revenue's template. But the revenue will not trust the bar codes used on forms like these, which must again be keyed in by hand. It is no good thinking you can fax your form over, however, as these will not be accepted. "With our faxes, they'd probably get jammed up," says Alain glumly.
Most returns are relatively simple, and the figures can be entered on the computer in a few seconds. The software can perform a preliminary check immediately, which should flash a warning sign on screen if the figures entered are obvious nonsense.
Despite this, offices like Woolwich do occasionally present ordinary taxpayers with demands for heart-stopping amounts such as pounds 24m, when the true figure is a tiny fraction of that. Barry and Alain say this arises from simple human error, as a hard-pressed operator fails to register the warning and approves the entry anyway.
Perhaps, I suggest, the warning should be a little harder to ignore. Why not sound off a siren throughout the room and set off the sprinkler systems, for example? Alain does his glum face again. "That'll be the next thing," he says.