Welcome to the forum Pj.
The 1st Bn were already in Singapore in 1940 so your grandfather would have joined them there from UK. I'm sure someone else will come up with information on where he would have been in the UK and when and how he went to Singapore.
I have turned your photo for you and attached it with this reply.
Have a look at this photo page
http://themanchesters.org/forum/index.php?topic=610.15 at the bottom are 2 photos of groups of POWs in Singapore the few that have been identified are all from 1st Bn Manchester's you may find your grandfather in one of them. These photos do not have all the Bn in them.
If you PM me with an email address I can send you high res versions of them.
Cliff
Modified to add a photo of a group of men taken at Ashton Under Lyne, some in this are also in the one you posted so I thought it may be of interest.