Now I have done a search - the report is only available from Kellogg's or ASA and after reading this statement from Kellogg I would have to question their methodology...
www.kelloggs.co.uk/whatson/pressoffice/News/kelloggs-and-swimming/government-urged-to-prioritise-the-sport-that-saves-lives#_ftn1
They asked councils the level of 25m attainment and it ranged from 26% to 91% - overall a third can not swim 25m
Then they surveyed 1003 parents of children aged 6-15yrs
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'A third of primary school leavers can not swim 25m'
Presumably from the attainment information from LA - they had good responses to their request (over 70% of LA responded)
However it is not clear if they asked the councils the percentage of children offered lessons. With academies and privately educated children not following the NC it can not be assumed that 100% of children were offered lessons.
'39% of children who could not swim were not offered lessons'
I have read the Kelloggs and ASA press releases and its worded as above 'children who could not swim'
NOT children leaving primary school who could not swim
NOR could not swim 25m
This is a bit of clever marketing as it you could assume that its 39% of the third of children they have already spoke about as leaving primary school who could not swim 25m but it may well be from a different set of data than that set of children.
And you can't correlate the two because the children in the survey are 6-15yrs and thus a proportion are arguably not expected to swim 25m for another 5yrs (the 6-11yr olds).
So I would like to withdraw my previous comment as I now doubt that any conclusions can be draw effectively from that report and I really should have known better 
I may be wrong but as ASA / Kelloggs have not shared their results in full then I can only presume from the data they have offered.
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So back to OP - this is obviously bothering you so I would suggest that you consider becoming a school governor - it's the only way to understand why these things are being asked of you.
I personally still think that the money is better spent elsewhere and provision is targeted to those children who can not swim.
Believe me - my son swam 400m last week - he does not need 24hrs of next term to be spent on swimming... not when he made absolutely no progress at in reading, writing and maths last school year....
The LA may, atleast let me opt him out this year - the school will be so relieved!!!