My idea a few years ago was to do away with the 1p and 2p because they are comparatively expensive to make and fiddly to deal with, and have the 5p as the smallest denomination in regular use, as is already the case in some countries (I think NZ and Australia have 5c as their smallest in-use coin). But with a just-for-fun and British quirky twist - have it renamed as a 'Shilling' (dually featuring both '5' and 'Shilling' in the design).
Items could then be priced in Pounds and Shillings if so desired, but it would still be decimal and technically nothing would change, there would still be 100 pennies in a pound and the 5p would still be 1/20th of a pound just like it and the shilling always were. Merchants could price exactly the same as now, e.g. £3.40 or they could be brave and price as £3/8 for the novelty value. Most would no doubt stick to the way it is now, but it would be fun to have pounds and shillings, and perhaps shillings could catch on at least colloquially.
The 10p could be called a florin and the 20p a double florin. The 50p would be 10 shillings, obviously.
I think it would be fun thing, but it's no doubt too late to re-establish any kind of shilling now, even in name only, for 2 reasons -
1. People who fondly remember using actual shillings are becoming scarcer so there really isn't much nostalgic connection with shillings, florins etc among the general public as a whole and the concept of having £1 made up of 20 of something would be confusing for many. And..
2. Physical cash in everyday use for payment of most things is being overtaken by electronic alternatives, so use of actual cash is dwindling and is very likely to continue on a downward trend.
Pie in the sky. Maybe it could have worked 20 or 30 years ago!