If your item overhangs one pallet, you can book space for two pallets to accommodate this. However, pallets are lifted by a forklift, which are only able to lift one pallet at a time. The maximum extra space allowance is two pallet widths (2m) and the goods must still sit within the 1.2m depth:
The usual size, weight and height restrictions still apply, depending on whether you're using a full, half, or quarter pallet. Your goods should be secured to the centre of the pallet:
You can then book and pay for two pallet spaces and your one physical pallet can be loaded in to the lorry with the goods taking up the space either side:
Booking extra space should allow you to avoid incurring an excess dimensions surcharge with the carrier.