I have a personal favourite of mistakes he made in closures as Uckfield-Lewes which was primarly closed for a road to be built. Talking of roads the Transport Minister at the time was Ernest Marples chairman of Marples/Ridgway road construction contractors.
Half right - the Lewes relief road was approved by Marples - but the railway closure wasn't.
http://en.wikipedia.org/wiki/Wealden_Line
To facilitate the road scheme, the British Railways Board (BRB) applied to Parliament for authorisation to re-route the line to Lewes via the alignment which had been abandoned in 1868, the so-called "Hamsey Loop". Approval was granted by section 4 of the British Railways Act 1966 which permitted:
A railway (1,586 yards in length) wholly in the parish of Hamsey in the rural district of Chailey commencing by a junction with the railway between Lewes and Cooksbridge at a point 365 yards south of Hamsey level crossing and terminating by a junction with the railway between Lewes and Eridge at a point 425 yards north-east of the bridge carrying last-mentioned railway over the river Ouse.
The new route would cost £95,000 to construct, and a request for funding was submitted to Parliament in 1966. This was turned down and the strategic function of the Uckfield line as a link to the south coast was effectively lost. BRB saw little further use for the line and applied for its abandonment.
The Conservative government lost the General Election of 1964 to Labour. By 1966 the Transport Minister was Barbara Castle, who also approved the closure of the GC Mainline (which was not recommended or proposed by Beeching).