Convert date text to Excel date

I have a list of dates in my spreadsheet that were copied (from an html file) and pasted into it. Therefore,this information is text. I would have thought it simple enough to convert this to excel date format (ie. numeric) that I can then manipulate as much as my heart desires! But no. I've tried, searched and cannot find a solution and I have a suspicion (hope) that someone here will tell me that it's quite simple? The date text as an example is: "Saturday 18 August" (without the quotes of course). I tried adding '2012' to these dates and then attempted to convert and that didn't work either.