A consultation has been launched on proposals to change imperial measures of spirits sold in pubs and bars with metric.

The changes have been driven by concerns over the availability of approved optics and thimble measures that measure one fluid ounce - one fifth of a gill - quantities of gin, rum, whisky, vodka and brandy.

They also aim to tackle the issue of ’free pouring’ into measures that have not been ’stamped’ - presenting a risk of selling inaccurate measures.

The Office of Fair Trading is proposing a new metric quantity of 25ml for sales of spirits, while fortified wines will be sold in quantities of 50ml or 70ml.

These would mirror the legal quantities in the UK. There will be a lead-in time of at least six months.

Similar proposals were shelved by the OFT following the last consultation four years ago.