You don’t need a licence to hand out leaflets in the city centre. You must, however, not obstruct roads or paths, and be careful not to block any shop doors or fire exits.
If you see any dropped leaflets you must pick them up. If you don’t, you could incur a fine per dropped item.
The same rules apply to handing out samples to the public. However, you must have permission from the county council if you want to place a kiosk or stall.