If you can't wire a plug this is not for you! It may also violate electrical safety regulations, that is all the safety advice I am giving. Editing this caused me to come up with a simple safety addition to the UK to European Adapter, see step 3. (2022, I've now seen these being sold commercially, again I regret my licensing option but I see this as validation of the idea)
This came about as I married a European. Naturally all her electrical equipment came fitted with European plugs, for the big stuff, toaster oven, iron, hair dryer( yes that looks sexist whilst I did already own an iron and a hair drier they weren't hers) etc it was a case of fitting UK plugs. For the gadgets (all those different chargers) Thankfully she already had them plugged into an extension cord. I change the plug on that and instant UK to multiple European socket adapter. As we've been married a while most of her gadgets have been replaced so this cord lives in the spare room for when family come to visit. We now have the opposite problem as do any UK families going on holiday in Europe. The answer fit a European plug to a UK Extension cord and keep it in your suitcase. I got my brother in law to take me to a hardware shop, but I have just discovered the camping section of go outdoors in the UK sells replacement European plugs.

Step 1: Back Ground Info

those less traveled may not realise that the UK and the rest of Europe don't use the same plugs and sockets. The UK uses a 3 rectangular pin design the plugs also contain a cartridge fuse. This design was adopted just before the UK joined what was then the EEC as at the time mains voltage was slightly different to that in mainland Europe. The single longer pin is the earth pin it slides an insulator out of the way of the 2 live pins it is theoretical impossible to accidentally connect to the live sections of a UK socket.

Plugs and sockets are not identical across Europe either. The 2 live pins are the same across the rest of Europe even in Russia and the Ukraine, because of this phone chargers etc and 2 pin plugs work anywhere. It is when there is an earth connection on the plug that the problem arises. There are at least 2 variations for earthing. A pin in the socket or side contacts. The plug I acquired works with both, a plug designed for just the pin style socket will connect with the power on a side earth contact socket but not with the earth contact. However one designed just for just the side earth contacts will not go into the pin earthing design.

Step 2: UK to European Safety Improvement

The basic idea is to put a UK plug on a European extension cord. The 13 Amp fuse in the plug means even if you do plug too many high powered appliances into the extension sockets the fuse in the plug goes not the whole ring main. European sockets have live contacts relatively open to the world, a paper clip or hair pin could get poked into one with little trouble, dangling charms on brackets could also. unlikely but possible causes of electrocution. Replacing the standard plug for one with a built in RCD (residual current device) helps protect against this,and use with wet hands, spilt tea & wine etc.
Whilst I wouldn't deliberately stick a chisel onto the cable to prove it works, I have run the cable of an electric lawn mower over and the RCD cut the power before I'd noticed that I'd done it.

Step 3: Extra Safety on the European to UK Version

This is something I've only started to consider. The loss of the fuse from the plug whilst making it no worse than a standard European extension cord does give rise to the possibility of over loading. In theory it should just trip the ring main and you get an annoyed handy man complaining about your appliances. Fitting a fuse or circuit breaker into the body of the socket bar shouldn't be a problem. The built in insulators across the live sockets makes accidental electrocution less of a possibility, but wet hands and spilt drinks are still there. As UK extension cords don't normally come with an RCD this is probably a low risk. I couldn't find a European plug with one built-in on line, I'll have to ask my brother in law if they exist. I did find an in line fixing one. While this might be health and safety gone mad,but as I proved once with a lawn mower you never know. A follow up instuctable may happen.