THE first week in July brings international collectors and museum curators to London for the summer auctions at the leading salesrooms. Over the past several years, the dealers and independent galleries in Mayfair and St James’s have used this as an opportunity to showcase their own material.

”London Art Week” is now very much part of the calendar. Whether you are a serious collector, a first-time buyer, or an interested passer-by, you can get to view the best of what can be seen outside a museum or private home. London is, as HM Revenue knows well, the centre of a trade in art which is now global.

For his July exhibition this year, Sam Fogg has works from the English medieval period which he has found and brought together over two decades. The earliest piece that I spotted is a delicate copper-alloy cross with segmented interlace, one Carrick Bend after another looping across little more than a three-inch arm; it is reckoned to date to the middle of the ninth century, predating King Alfred by a generation.

At the other end of the period come the distinctive pottery ware of the years before the Reformation and a delightful stained-glass roundel depicting a woman bent over to cut hay, sickle in hand. One of a series of the Labours of the Months which commonly appeared in church windows depicting Creation, it is a foot in diameter and comes from Norwich (c.1525).

The Berger Cope laid out flat

In her little world, her neck-scarf is looped over her black bonnet to hold it in place, and her simple purple tunic is caught at the waist. Behind her she has placed a jug. No doubt, when the hour strikes on the clock tower beyond she will pull out the stopper to refresh herself on a hot August day. Even in her stout black shoes, there will be no running across the sharp stubble.

Not all the art has survived the ravages of time or the iconoclasm of sectarians at the Reformation and in the Puritan period. The Tavistock breviary (possibly illuminated in Oxford or Devon, c.1310-20) is the companion to the New York volume now in the Morgan Library (M. 329). It includes a stag with a cross in the lower margin which link it to the Church of St Eustace in Tavistock.

Attributed to John Wattock (active in Norwich, 1495-1540), the August roundel from a series of the Labours of the Months, England, Norwich, c.1525

The alabaster sculpture of the Trinity, thought to date from the reign of Henry IV, would have once been part of a retable. It has been violently damaged; Christ on the cross held between his enthroned Father’s knees suffers a second indignity, as his face has been hacked off and he hangs there limbless.

Such destruction makes undamaged survivals all the rarer. Nicholas Mullany, around the corner at 11 Bury Street, has one such Nottingham alabaster depicting the Nativity. The Virgin kneels next to a crib that has been turned into a golden aureole in front of which the Christ-child, already holding the vexillum of the resurrection, stands.

Lined up behind her, the three wise men behind a balustrade seek to peer over the Virgin’s over-large halo, which looks more like a sun hat than a sign of her humble sanctity. Rich details of the original polychromy suggest how the altars of England would once have blazed with light.

“Medieval Art in England” is at Sam Fogg, 15d Clifford Street, London W1, until 26 July. Phone 020 7534 2100. www.samfogg.com