The health service faces a bill of millions for reminding patients of their legal right to choose their own secondary care provider under the terms of the NHS constitution.
A Department of Health impact assessment reveals it could cost as much as£31.9m nationally or£210,000 per primary care trust to provide the information on choice.
DH economists say to break even PCTs would have to ensure seven in 10 patients switched to a provider "more aligned to their needs".
Even under the best case scenario of a cost of£5.2m per year (£33,000 per PCT), 5.5 per cent of patients would need to switch provider.
But DH survey figures released this week show fewer than half of patients remembered being offered a choice.
The news comes amid growing concern that PCTs do not have the power to hold providers to account on choice. At a DH conference last week co-operation and competition panel chair Lord Carter queried if PCTs could ensure patient choice.
At present, PCTs can pay GPs extra to co-operate through local incentive deals - but HSJ understands the DH hopes to negotiate choice into the core GP contract.
This would mean PCTs could impose financial penalties on non-participating GPs.
PCT Network director David Stout said current arrangements with GPs were "largely based on goodwill and exhortation". He said: "If it were contractually based, it would be easier."
East and North Hertfordshire PCT chair Pam Handley said it would be "unfair" to require GPs to act without also requiring hospitals to increase their flexibility. She warned the added financial pressures could knock PCT strategies.