Rosie Millard in Milan: The Last Supper was in a terrible condition

The work, painted on a monastery wall in Milan, will be on display from May 27.

Exclusive preview access to the restored masterpiece, which is already dividing the art world, was given to the BBC's Nine O' Clock News programme.

Bold step

The old master used an experimental fresco technique and as a result the painting started to flake away almost as soon as he finished it 500 years ago.

Some critics say too much paint has been removed

Now a marathon £5m restoration has attempted to save it from disintegrating completely.

Restorers have taken the bold step of stripping away all the paint from previous restoration attempts.

Bare areas of plaster were then painted in with watercolour.

Pinan Brambila, head of the restoration team, said the painstaking work had revealed formerly hidden detail.

She said: "Many faces were enlarged so they had a different physical structure. Some eyes had been rubbed out and painted over with small brush strokes.

"Underneath we found the original eyes - the eyes as they were originally painted."

Photographs of the painting taken in the 1940s show it had been in dreadful condition, but now lines which were crude and inexpressive are delicate and refined.

Pollution precautions

The food on the table and the creases on the cloth can now be seen clearly.

The mural is still far from perfect, and some critics feel too much paint has been removed.

Visitors are expected to flock to see the restored masterpiece

However, others say it is probably nearer to the original that da Vinci painted.

Oxford University's Professor Martin Kemp said: "The gains are that we now have a much better idea of what Leonardo's picture would have looked like from the surviving details, but we know that recovering what it looked like in total is in a sense an impossible job, so what has been fabricated is a late 20th century picture on the best information we have."

Restorers have also taken possible future pollution of the masterpiece into account.

Visitors wanting to see it will have to pass through a glass tunnel and several pressurised chambers, walking on anti-bacterial carpets while a stiff breeze blows any dirt or dust from their clothes.

It is estimated that nearly half a million people will see the painting this year when it is put on public display again.