If you are travelling to the UK, and you do not have chip and PIN in place at home, you willl still be able to pay for goods and services in the same way as at home.
If you are using a non-chip and pin card issued by an overseas bank they you will still be able to sign. The terminal will read the card and instruct the retailer to ask them for a signature rather than a PIN.
If you do have chip and PIN at home then you will be prompted to enter your PIN. However, when you use your chip and PIN cards in shops which have not yet upgraded to chip and PIN equipment, they will still ask you for a signature.