Top port (and sherry) in a storm

You could call it a belief, I suppose: that the greatest wines of all may, from time to time, be eclipsed by fashion, but that they will never disappear altogether.

Sooner or later, they'll be back. Sooner or later, we will all understand, and fall on them in dribbling avarice. My job (and this is where a beam of light shines down from between the storm clouds) is to take the word into the places of darkness.

The Don's basement bistro is a place of relative darkness, and I certainly felt the beam of light on my neck as I sat down there recently. Or so I thought. On closer observation, the beam appeared to bypass me completely and plunge straight into my gleaming, straw-gold glass. I can't blame it; this was Grail-grade wine. "Sandeman Rare Fino Sherry, Limited Release from Selected Casks", it was called. "Bottled in Spring 2000". Each tiny sip seemed to set off a small landmine in my mouth, leaving shards of wine vaporising pungently. Sip for sip, nothing on earth could be quite as bracingly mouthwatering as this.

Perhaps the ghosts of the place had something to do with it. The Don occupies what are, for the London wine trade, genuinely historic premises in tiny St Swithin's Lane, almost opposite Cannon Street station. Mark Lane, which was once to the wine trade what Fleet Street was to the newspaper business, lies parallel, half a dozen streets away. It's hard to believe now, but for almost 200 years this was where George Sandeman and his heirs and successors bottled pipe after pipe of port and madeira, and butt after butt of sherry, rocked up from the river in carts.

Belief is made easier by the fact that a large 1945 photograph of the rack of butts occupies one end of the bistro - and at the top of the stairs is the Capital Patent Crane with which these killingly heavy casks of wine were lowered into the ground (a pipe of port means nearly 60 cases). The stairs themselves, complete with cask guide rails, are listed, though tedious safety regulations mean that they are now interred beneath another set of greater bureaucratic conformity. Outside the building, meanwhile, swings the original Sign of the Don, freshly returned from a 30-year Portuguese exile in the Sandeman museum in Oporto. This caped crusader, one of the greatest of commercial images, was originally drawn for the company by George Massiot-Brown in 1928. Rumour has it that it will soon glow.

The Don has a ground-floor restaurant, reviewed by my colleague Fay Maschler on 5 December, as well as the subterranean bistro; Fay ate from both menus. It was the potential for discovering great fortified wines which drew me there, and this side of things got off to a good start with the magnificent Limited Release Fino described above (£3.95 for a 75ml glass), replacing Sandeman's Bone Dry Old Amontillado (£3.25), which had temporarily run out. Knowing how well fino goes with food, I felt disappointed that there were not more to choose from. Happily, this deficiency is about to be remedied, with a modest list of seven, including a Puerto Fino (£2.50) and a Manzanilla Pasada (£3.95) from Lustau. As it was, I drank (with a quietly flavoured terrine of grilled vegetables and a barely moistened bouillabaisse) the 2000 Trinity Hill Sauvignon Blanc, which was crisp and fragrant, though a slighter drink than great sherry. It comes from owners Robert and Robyn Wilson's own vineyards in New Zealand.

Then on to port. Every day a different vintage port is decanted by sommelier Richard Fergé; furthermore, there is also a list of 30 different vintage ports which can be ordered for decanting in advance, including 10 Sandeman vintages back to 1911. Some of these are Sandeman museum stocks and were actually bottled in the brick vaults which the bistro now occupies. Port of the day was the now-limpid 1970, its scents and flavours evoking rose petals and tea chests (£8.75 for a 50ml glass). There are, of course, cheaper port options, like the Sandeman 1994 LBV for £4.25 or a glass of Sandeman 20-year-old tawny for £8.25.

I hope the Wilsons remember, too, that Sandeman once shipped madeira. Vintage madeira is actually even greater and more intense than either vintage port or fine old sherry. Since almost no one serves it, almost no one knows about it. The Don has a glittering opportunity to become the first restaurant in London to serve half-a-dozen vintage madeiras by the small glassful. Madeira doesn't spoil once opened, so it isn't even logistically difficult.

Experience of The Don encouraged me to step out and about to see who else takes fortified wines seriously. Of course: the extraordinary Gordon's Wine Bar; how could I forget? "Taken seriously" here means, above all, served copiously, which is surely one of the reasons why Gordon's is so popular with young bohemians. At as little as £3.20 for a tumbler (which must by my reckoning contain at least 200ml) of sherry, port and madeira, this must be one of the cheapest places in London to rearrange reality. Gordon's extraordinary vaults add to the appeal (going for a drink here resembles pot-holing). I called, of course, on a wet night, and was somehow reassured to see that it was raining under the pavement, too, albeit at a much slower rate. The port, sherry and madeira which come anonymously out of the barrels are of modest quality only; better choices (such as Taylor's deeply plummy LBV 1994 or even Messias's faintly toffeed 1985 vintage) are no less keenly priced (£5.50 and £6.70 a tumbler respectively). "Righteousness exalteth a nation," said one of the old Victorian framed prints dangling squiffily from the walls. So, visibly, doth cheap port.

Another destination where fortified wines are respected is the Davy's extensive chain of wine bars. I once recorded a radio programme in Davy's Greenwich cellars and was astonished to see how colossal were their stocks of ancient vintage port. Alas, many of these have now been sold, but they are still hoarding vintage port back to 1912, so it's worth asking what you might be allowed to have decanted for a special occasion. The list I have seen includes some of the great '45s, '47s and '48s. At a modest level, I relish Davy's Finest Manzanilla (£2.35 for a 125ml glass or £6.95 per half bottle) - soft, supple and deliciously gingery, and the perfect accompaniment to Davy's excellent sandwiches.