After 14 February some retailers may refuse to accept payment from people using chip and pin cards if they do not know their pin number.
Nearly 130 million chip and pin cards have been issued
During the introductory period of the chip and pin system, retailers have been able to accept a signature after first checking with the card issuer.
After 14 February, banks and retailers have decided to curtail this facility.
Consumer groups say that many disabled people find it hard to remember their pins and may be turned away at tills.
The Association of Payment Clearing Services (Apacs), which has overseen the chip and pin programme, said people who had forgotten their pin numbers should ask their card provider for a new one.
Consumer bodies and charities such as Age Concern are concerned that people suffering from visual impairments, degenerative brain diseases such as Alzheimer's, or those who find remembering numbers very difficult are being left behind in the move to chip and pin.
In total, the National Consumer Council (NCC) has estimated that up to three million Britons could have difficulty remembering their pins.
But Apacs said that people who had genuine difficulties could apply for a chip and signature card.
To date, 100,000 chip and signature cards have been issued, compared to nearly 130 million chip and pin cards.
In addition, there have been concerns raised over the estimated one in 10 of the UK's tills that are still not able to accept chip and pin cards.
But Apacs told BBC news that this did not matter.
"If you have an old style non-chip and pin card or present your card at a till that has not been converted then you will still be able to use a signature," Sandra Quinn, spokeswoman for Apacs, said.
Chip and pin cards aim to cut fraud by including a smart chip, which can store more information than the usual magnetic strips, and also by having users verify transactions by keying in a pin number rather than signing a receipt.
Over the past two years card issuers have been busy replacing all credit and debit cards in the UK.