If you locum at a GP practice for more than 6 months then you can no longer be classed as a locum (for NHS superannuation purposes) in that practice, and would have to become a Type 2 GP.
According to the NHSBA Locum Factsheet (September 2016):
After six months of working in the same practice:
"You can still work under a contract for services arrangement; your surgery is not legally obliged to employ you under a contract of service."
And according to the NHSBA Form GP SOLO (April 2016):
"[Form GP SOLO applies] to NHSPS Employing Authorities including OOH Providers and CCGs who engage the services of GPs on a self-employed/fee-based/contract for services arrangement."
You will then be able to pension 100% of the fee paid as opposed to 90%.