Last time I visited it, it was in the Eden centre, opposite the bus station and Apolo centre. Get off the bus, cross over to centre and walk right around to the other side, it is on the bottom level, halfway down as if you were heading into centre of LC. Or if driving, best place to park that really manky dusty carpark by bus station, and same advice, head down the road as if going into LC and it'll be on your left . If this is too vague , let me know and I'll try to be more specific!
If you can fill in the forms when you are there, they deal with it there and then, or you can go back. Very quick and painless, (except for the queuing time!!)