Diversions will be in place from later today as road improvements begin on the A34 at Chieveley.
The work is expected to continue for a week. The slip road from the M4 at junction thirteen will be closed from 10pm tonight until 6am.
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The Duchess of Cambridge has been driven to St Mary's Hospital in London in the "early stages of labour", Kensington Palace has said.
The Duchess of Cambridge has been on maternity leave since the week before Easter.
The Duke and Duchess of Cambrige have been together for 15 years and will have three children under the age of four.