This is not uncommon here, a lot of pallet freight goes via pallet networks and sub-contractors.
It would not be unusual for a single pallet consignment to arrive via several different DC's and several hauliers.
It is also very common for the transport to be curtainsiders here which are not pestproof in my book.
This is common across the industry in the uk.
I can absolutely confirm this to be the case. It's partly/mostly a price thing, and partly a practicality thing.
If you want to order less than a full load, you could commission a van or truck to deliver it direct to destination at a cost of £hundreds, or you could send it via one of the numerous pallet network systems for potentially under £50. This can make a very significant difference to the per kg / per unit price of the product once delivered.
Unless you are based extremely close to the delivery point, the vehicle on which you load the product will almost certainly be a different one to that which delivers it to the recipient, and indeed it's probably operated by a completely different business to the one that the supplier actually pays - many of these networks are lots of independent members who collaborate through one system as it benefits them all. In some cases such a delivery can change hands via 5-10 different "hubs" on its way across the country, all of which could be handling pretty much anything.
There are a few more food-centric groupage systems/networks, but they're more expensive, less flexible, capacity is more limited (to the extent that in some regions you'll often have to be able to put a huge amount through them such that you can tempt them to run more vehicles, or they simply won't deal with you), and it still doesn't guarantee an absence of potential contaminants - e.g. a lot of sites don't like glass or specific allergens on the vehicle, but food-only services can often be carrying drinks products in glass or packets of peanuts etc.
The thing that always strikes me as rather incongruous is the mismatch between this side of the supply chain, and the often very stringent requirements (slowly tending towards "vehicles must not be driven by anyone whose second cousin's ex girlfriend once saw a photograph of a man looking at a peanut") that go with it, as compared to those on the final leg of the retail distribution journey. Look at the delivery of finished goods as they arrive with the retailer - mixed loads on roll cages with ambient vehicles carrying food along with a delectable assortment of household cleaning products, toiletries, cosmetics, and over-the-counter pharmaceuticals. Or fresh produce in open cases on lorries with houseplants and flowers. Or chilled cages of meat products, often poorly wrapped or prone to damage/leaking, directly next to cases of finished chilled RTE goods.
In your position I think you have two possible approaches, and it's probably worth exploring both of them.
1) Talk to your suppliers about delivery options. They should be able to find alternative services, but equally these are likely to have a cost that someone has to cover.
2) Risk assessment. What is the actual potential for contamination, for the products you're handling? Are these all sealed such that neither liquid nor solid contaminants can actually contact the food itself? Does your goods-in inspection really detect all potential contaminants that could actually cause a food safety risk? Obviously taking such an approach is far from ideal and can very difficult to defend at audit, but presumably your suppliers have done just that, so the first stage is probably to point the question at them - can they share their risk assessment / evidence that the delivery method doesn't pose a risk to the products with which they supply you?
