Visions of Paradise: Botticini, National Gallery ★★★★★

The resplendent blue, red and gold Palmieri Altarpiece, completed by Botticini in 1477, is a truly monumental panel. Named The Assumption of the Virgin, the piece was intended for the funerary chapel of Matteo Palmieri, historian, poet and all-round man-about-town. Originally attributed to Boticelli, the panel would have hung in the long-vanished church of San Pier Maggiore in Florence, which now houses a modern marketplace.

The altarpiece, which has been out of sight since 2011 for research, is the centrepiece of a new free exhibition at The National Gallery, made up of around 30 other works from the period. Standing before the panel, we see a broad panorama of Florence and its surrounding countryside, rendered by the artist with astounding detail and accuracy. The painting is dominated by the gilded dome of heaven, populated by legions of angels and saints. Palmieri himself kneels in the foreground, with his cap fashionably slung over his shoulder, gazing as the Virgin Mary ascends to heaven.

The scholarship that has kept this altarpiece out of public view is plain to see. In a fascinating video the beginning of the exhibition, Dr Jennifer Sliwka explains how she and several members of her team travelled to the former site of San Pier Maggiore and discovered remains of the medieval church in the modern buildings. Sliwka shows us gargoyles looking out over modern streets, the crossed Keys of St Peter on shop walls, medieval carvings in the bathroom of a cafe and part of the belfry in a modern apartment building.

However, some of the exhibition's additional components seem unnecessary. San Pier Maggiore's other altarpiece, created in the workshop of Jacopo di Cione in 1371, completely steals the show. Many more visitors were examining this polyptych than Botticini's own panel. The final room, where visitors were instructed to spot stylistic differences between different painters, was fussy and overly academic. The section on Palmieri's posthumous charge of heresy was surplus to requirements.

For the video and altarpiece alone, though, it's worth stopping in on this free exhibition next time you're in Trafalgar Square.