The problem with the Royal Albert Hall - designed and built by military engineers Francis Fowke and Henry Scott in a pared-down antique style borrowed from architect Gottfried Semper in Albert's Germany - is that it is a complete free-standing oval object. It is aesthetically very difficult to extend. Originally it connected to the giant glass conservatory of the Royal Horticultural Society's gardens to the South, which acted as a palatial entrance with restaurants, lavatories and suchlike. But the gardens were a commercial failure. The glasshouse was demolished in 1889. Since when, the Albert Hall has been squeezed for space.

Only one above-ground addition will now be made: a new south porch, the same size, style and materials - terracotta and brick - as the three other existing porches, will be built at the point where the connection with the old glasshouse used to be. These porches are little buildings in their own right, and the new one will house a restaurant and act as an important new entrance. You probably won't even notice it.

For this is the very opposite of signature architecture. The work, led by Martin Ward of architects BDP, a veteran of the Royal Opera House project, is highly ingenious and in places structurally audacious, but the whole deal is not to show the effort. Bit by bit, the auditorium is being brought up to scratch with new seating. Work on replacing the leaky old glass roof is underway. The foyers are gradually being opened up. The huge neglected ambulatory of the top-floor gallery will be brought back into full use. The mighty Willis Organ alone will cost £2m to restore. The acoustics will be improved. If they can find the money, the surroundings will be redesigned, forming uncluttered space between the Hall and architect Nick Grimshaw's smoothly curving proposed extension to the Royal College of Art.

Most importantly, it means the Hall will be able to spend its increased future income on productions, not on sticking-plaster maintenance. In recent years it has tentatively started to originate and co-produce productions rather than merely receive them: this will accelerate. Chief executive David Elliott says: "We will be able to invest our income into programme ideas, true to the original remit of the Hall. And we want it to be open to visitors all day."

The programme will still be about 75 per cent music - with more jazz than previously, and more big children's events. Scientific spectacles - as called for by Albert - are being planned. Straight drama is more difficult - the acoustics don't suit the spoken word, and 5,000 plus seats are a challenge for any play to fill - but even so, some theatre directors, beguiled by the intensely focused space, have been calling round, says Elliott.

It's been called, accurately, "the nation's village hall". What's true of a village is true of a nation - when the hall falls into disrepair, the community is in trouble. Which makes this vast, gradual restoration project more than a merely technical achievement. It's a matter of old-fashioned national pride.