Firms making e-cigarettes could be ripping off customers - with research showing refill cartridges are being sold for around £1.50 (NZD$3), despite costing only about 4p (8cents) to produce.
This means customers are paying roughly 37 times the cost price, when typically consumers pay around eight times the cost of manufacturing a product.
Now campaigners have raised concerns that the mark-up means taxpayers could lose out if the NHS finalises a deal thought to be under discussion for British American Tobacco to supply prescription e-cigarettes.
Jonathan Isaby, chief executive of the TaxPayers' Alliance, said: 'The NHS has a terrible record of negotiating a good price, despite its scale as a buyer.
'It would be important to remind those involved in the negotiation that in times like these there is absolutely no scope for the NHS to tie itself to a contract which delivers anything but the best value.'