To know what you should get, use the red button on BBC TV. Go to 'Business and Markets' then 'Foreign Exchange' and click on 'Tourist rates'. This will show you the latest figures on what to expect at most High Street Bureau de Change, rather than the higher 'official rate' as shown on the links.
A reasonable rate at the moment to convert pounds to euros is about 1.14 (ICEplc - a good online provider - is offering 1.444). This means 100 euros will cost you £87.38.
However your question asks "100 euro converted in pounds". If you offered 100 euros to convert into pounds you would be lucky to get an exchange rate much better than about 1.25 - that is about 80p for each euro. This means you will get about £80 for your 100 euros.