There are several access card schemes available, with varying levels of coverage.
Ecotricity operates the Electric Highway scheme, mostly serving major trunk roads and motorways. These high speed charging points are often at service stations. The cost is £10 per year.
The Polar network incorporates Chargemaster charging points, along with those of certain regional networks. Access charges are currently £10 per year, but set to increase soon.
AlphaElectric, operated by leasing company Alphabet, is a solution offered to fleets that incorporates 85% of the charging points available in the UK, via Polar and regional schemes. Billing is managed as part of the agreement.
These regional networks, created on the Plugged in Places scheme, are slowly beginning to merge, but there are still several available. These may be suitable if your travel is limited to one area. Small access fees apply, dependent on area.