The fake building blocks, which were destined for the streets of the UK, arrived in Stansted last month.
Officers discovered 2,315 figures and assorted kits, many of which related to DC Comics and Marvel characters like Iron Man, Batman and Spiderman.
The goods, which had been listed as plastic blocks for decoration, had been sent to the UK from China in four separate packages with a declared value of just $365.
An investigation was launched by Border Force and LEGO has now confirmed that all the goods, which will now be destroyed, are breaches of their copyright.
As the rights holders, the company can now decide whether or not they wish to prosecute the importer privately.
The seizure follows a discovery last month of nearly 500 items of counterfeit Disney products carrying images of characters from the film Frozen.
Phillip Holliday, Border Force Regional Director, said:
Although the goods were not branded it was quite clear that these were poor imitations of genuine products, a suspicion that was quickly confirmed by the companys legal department.
Smugglers are not concerned with the commodities that they deal in, only what will make them a profit.
The challenge for Border Force is to stay one step ahead of the smugglers.
We are determined to crack down on this crime and we have officers working 24 hours a day at ports, airports and mail sorting centres identifying counterfeit goods before they reach the streets.
Members of the public can help to disrupt this trade by ensuring they only buy from genuine retailers and our advice, as always, is if a price appears too good to be true, it probably is.
Anyone who has been sold counterfeit goods or knows someone who is selling them should contact Action Fraud on 0300 123 2040.