Hi freefee,
The DWP cannot force anyone to claim UC if they don't want to. I think it's unlikely that you will receive a Managed Migration letter but if you do you can ignore it. But I would first phone the Citizens Advice Help to Claim phone no which is on page 2 of the letter just to check that you will not lose out.
Even if you are entitled to just £1 of Universal Credit as it is a passporting Benefit it may give you concessions on all sorts of other things ( even Gym membership I am told ).
David
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
