2020 - whilst you may not worry about the exchange rate of the pound vs various currencies, it does affect you all the time.
Any products that you buy that are sourced from abroad, a lot of white goods, most food stuffs, etc etc will cost you more or less depending on the exchange rate.
If a supplier is having to buy something from the US it will be cheaper at the moment as the dollar is weaker against the pound than it has been for a while. If the dollar strengthens then the supplier is going to have to pay more and will pass the costs on. A very simplified example as there are many more market forces at work than just the exchange rate.
As to the original question, I think we will join the Euro before the Labour govt leaves power, Brown is better than Blair for being a Europhile, but not by a huge amount. My guess is that there will be no referendum on the issue and it will be forced through within the next couple of years. Personally, I don't really care - it'll just mean people have to do a lot of calculations to work out if something is worth it or not still. As long as companies don't use any confusion to ramp up their prices, then it doesn't bother me - it will increase our competitiveness in the European Market and make prices less vulnerable to fluctuation.