Work has started on the final link of the Channel Tunnel high speed railway from London to mainland Europe.

A giant boring machine, itself the length of a football pitch, will tunnel nearly 7.5 kilometres (almost five miles) from Stratford in east London to St Pancras railway station in the heart of the capital.

Progressing at a rate of 95 metres a week, the boring machine, nicknamed Annie, will shift 792,000 tonnes of earth - the equivalent weight of 88,000 double decker buses.

The machine - built by Teesside-based engineering firm D-CECC for Kawasaki - is expected to reach St Pancras, next door to King's Cross railway station, in about 20 months.

As the boring machine cuts its way through subterranean London, a giant screw fixed to the cutting head will draw soil away from the tunnel end. This waste earth will then be carried out along a conveyor belt.

The finished tunnel will measure 8.15 metres in diameter (almost the height of two double decker buses) and run about 24 metres below the surface.

On the new line (top of photo), the Eurostar will be able to run faster

In places Annie will have to steer a careful course, for London is almost as crowded underground as it is above.

At Highbury and Islington station, the tunnel will run about 9 m below the Victoria and Northern tube lines. At Caledonian Rd in Islington, it will rise to 4 m below the surface, and just 60 millimetres below a sewer at the same location.

A second machine, nicknamed Bertha, will soon join the effort.

Its job will be to tunnel in the opposite direction, clearing earth along an 11km stretch from Stratford to Dagenham.

The rail link is being built in two parts. The first stage, connecting Folkestone to north Kent, is 90% complete.

In July last year, work started on the final phase which extends the line under the Thames estuary and west, into the capital.

The 110km high speed line, which is costing �5.2bn, is the first major railway to be built in the UK since the Victorian age.

When finished in 2007, it will halve the journey time from the new station to the Channel Tunnel to 35 minutes. Trains will mirror the high speeds reached on the French side and the trip from London to Paris will be cut to 2.5 hours.