Thrift Wood, Bicknacre, Essex. Thrift Wood is a 48 acre woodland owned by the Essex Wildlife Trust. It is accessible to the public at all times. Link to Thrift Wood at EWT website. This site is famous for its colony of re-introduced Heath Fritillaries.

Devils Dyke, Cambs. An ancient defensive barrier across the chalk from Stetchworth to the edge of the Fens at Reach.
There is a public footpath along the top. Wikipedia entry . Restoration Project

Fleam Dyke, Cambs. An ancient defensive barrier across the chalk from Balsham to the edge of the Fens at Fulbourne.
There is a public footpath along the top with access at all times from each end and from a lay-by on the A11. Guide

Sugley Wood, Gamlingay, Cambs. A new wood on chalky boulder clay.
Free public access, with free parking along the side of the access track.
This site has a strong colony of Marbled Whites. Clouded Yellows were here in July 2012.

Woodwalton Marsh, Woodwalton, Cambs. A Nature reserve of the Bedfordshire, Cambridge, Northamptonshire and Peterborough Wildlife Trust. It is accessible to the public at all times. Link to BCNP website. It is only 1.8 acres but full of interest.

Therfield Heath, Royston, Hertfordshire. Common land. Steep well-drained slopes over chalk.
Free public access with a free car park.

This site had strong colonies of Chalkhill Blues and Marbled Whites.

RSPB Strumpshaw Fen, Strumpshaw, Norwich.
An RSPB Reserve. Free public access for RSPB members, otherwise payment is charged for entry. Free parking.
Part of the Norfolk Broads on the north bank of the River Yare. This site is known for its colony of Swallowtail Butterflies.

Ted Ellis Reserve, Wheatfen, Surlingham, Norwich.
Free public access. Free parking.
Part of the Norfolk Broads on the south bank of the River Yare. This site is known for its colony of Swallowtail Butterflies.

Glapthorn Cow Pastures, Glapthorn, Northamptonshire.
Free public access, with informal free parking along the side of an unpaved road opposite to the access.
An ancient wood on heavy soil. Managed by the Wildlife trust for Bedfordshire, Cambridgeshire and Nothamptonshire.
Large areas of Blackthorn specially managed for the Black Hairstreak.

Salcey Forest, Hartwell, Northamptonshire. Owned by the Forestry Comission.
Free public access. The main car park is open from 8.00 am - 7.00 pm. in summer (closing at 5.00 pm in winter).
The main car park is Pay and Display, £1 for an hour, £3.00 for the day.
This site is famous for its colony of Wood Whites.

Aston Rowant NNR, Stokenchurch, Oxfordshire. A National Nature Reserve.
Free public access. A free carpark for each side of the reserve, north and south of the M40.
This site features colonies of Adonis Blues, Chalkhill Blues and Silver Spotted Skippers.

Otmoor, RSPB Reserve and adjacent Roman road.
Free public access. A small, free car park at the end of Otmoor Lane, Beckley.
Known for its Brown Hairstreaks.

Whitecross Green Wood, Buckinghamshire and Oxfordshire (mostly).
A reserve of the Berkshire, Buckinghamshire and Oxfordshire Wildlife Trust.
Free public access with free car parking. There is no roadside notice. Turn off the road opposite to a small thatched cottage, go through two gates into the car park just inside the the wood.

North Warren, Aldeburgh, Suffolk. Owned by the RSPB.
Free public access through the public footpaths running through it and the areas of open-access land.
There is a large pay and display car park just north of Aldburgh by the coast road, giving access to North Warren by public footpaths, and a very small free car park off the Aldeburgh - Leiston Road.

This site is famous for its colony of Graylings.