I presume you are referring to streaming 'off the website' as the London Philharmonic Orchestra's website.If this is the case, then the answer is most probably no - unless, of course, they do allow you to specifically download it from their official site for free. Even then it is doubtful if you can still redistribute the download, or even copy it to any form of digital matter - mp3 player, cd, memory stick etc. Then there'll be legal implications for 'public performance' - which, in this case, would probably be breaking the law in terms of copyright infringement if you were to re-enact the piece or for distributing the piece publicly. Even burning the musical piece to a cd to play in a concert practise room would still be classed as copyright infringement as you would be creating a public performance. So, to cut a long story short - I highly doubt this would be legal, nor would I advise you to use the LPO's music publicly, not at least without prior written consent.