Wednesday's decision by Brian Mawhinney to go ahead with the construction of the Newbury bypass has again forced into the limelight the site of the first battle of Newbury in 1643.

That battle was an important turning point in the Civil War. The King's path to London was blocked, and although the battle itself was inconclusive, at Newbury he lost his last chance of returning in triumph to the capital.

The battle has a special personal interest for me because of my second name, Digby, which is a family name coming down through my mother's side of our family. An earlier member of the family, Lord Digby, was one of the leaders of the King's forces in the battle. It is no surprise, therefore, that as the MP for Newbury I take an almost proprietorial interest in the site of the battle.

Sadly, rather more than half the site has been covered in modern times by the housing estate of Wash Common. But what remains as open land is still large enough for the Sealed Knot society to have fought a reconstruction of the battle on its 350th anniversary in 1993. This part of the site has now been recognised as an official battlefield in English Heritage's new battlefield register.

Newbury's desperately needed bypass is due to cross the north-westernmost tip of the site. Although the battle itself was fought further to the south and east, the area crossed by the bypass was where the ends of the lines of some of the forces are believed to have been drawn up before the battle started. This has raised a number of questions as to whether the bypass will cause any significant damage to the battlefield.

In fact the route follows the embankment of the old railway, which means, sadly, that the lie of the land has already been irrevocably altered. Where the route leaves the old railway line, it turns away from the battlefield across ground which has already been crossed by another railway line, a canal and a new road since the date of the battle.

It is no great surprise that English Heritage has taken the view that the result of the 1988 inquiry into the bypass, which confirmed the details of the route, should be allowed to stand and that the new battlefield register did not warrant a reopening of the inquiry.

While my personal interest gives me a particular reason to be sad at how much of the battlefield was lost to the industrial revolution and to the post-war demand for housing, it seems clear to me that the line of the bypass will do no damage to the battlefield which has not been done already. It would be absurd to use it as an excuse to delay the relief from pollution and other environmental advantages which the bypass will bring to the people of our lovely old market town.

The writer is MP for Newbury and Liberal Democrat spokesman on local government.