Code To Generate 'date' Ref Number

each time a button is clicked I want a new ref number to be produced and displayed on my userform.
I can't however create the code to generate this ref number.

In column A of my 'sweeplog' worksheet is where I want the ref number to be placed. This ref number is simply made up of today's date - in format ddmmyy eg 240408 for today 24th April 2008 then add the number '1' if its a new date or the next number in coulumn A if not.

for example In column A I have these 3 ref numbers
A2 = 2404081 (24th April 2008 plus 1 as this is the first ref used today)
A3 = 2404082 (as above but with 2 added)
A4 = 2404083 (as above but with 3 added)

now tomorrow the next ref number that would be shown in column A (after the user clicks the button) would be as follows.....

A5 = 2505081 (25th April 2008 plus 1 as this is first ref used on 25th)

I am able to get this unique ref number to show in my userform but can't figure out how to produce the code to generate it