In reply to ablackett:
No. The plural of an abbreviation does not have an apostrophe.
Apostrophes are used for omission e.g. pick 'n' mix, but not for abbreviation, especially not capitalised abbreviation or dates e.g. MOTs not MOT's and 1990s, not 1990's
Useful website:
http://www.oxforddictionaries.com/words/apostrophe#apostrophes_showing_omis... and yes, I know it's an American site, but the same does apply in UK grammar. Hope this helps.