HMRC describes bills of lading as documents of title that evidence the contract between the exporter and the carrier. A sea waybill is similar, but it is not a document of title.
That difference matters when you are paying a new supplier. Agree in the purchase contract which transport document will be issued, who it names and when it will be passed to you. Then ask your freight forwarder how the carrier will release the container at the UK port for that document type.
Keep every transport document, including bills of lading and sea waybills, with your other records for the shipment. HMRC treats commercial and transport documents as part of your VAT records, which must be kept for at least six years.
Sources
A summary of the public sources above, checked when it was published. General information, not legal, tax or financial advice.