Lego is big on giving away free things when you buy enough stuff from its official shop, including a miniature version of Avengers Tower as it was seen in many of the MCU films. Normally these sets are only available for a short period of time, after which they never see the light of day again. Clearly that month-long promotion wasn't enough, because Lego has more to give away.
Details are available over on the Lego Store promotions page, and you have until 30th June to buy enough Lego to get your hands on. Sadly the amount is still a rather high £75, but this time the promotion applies to all Disney-brand Lego - not just the ones with a Marvel logo. In other words you can grab yourself the free gift for buying a Star Wars set, the new Lego Ideas Steamboat Willie, or even 26 of the new Disney blind bags.
Sadly it seems to be one per order, so spending £150 won't get you two Avengers' Towers to build or hoard. If you want more than one you're going to need to send off multiple orders with at least £75 of Disney Lego. The other free gifts stack however, and you can still get the mini Space Rocket Ride at the same time - provided you spend at least £85 on one go.
That deal is also available until 30th June, alongside double VIP points for anyone who buys 'Queen Watevra's ‘So-Not-Evil' Space Palace' and 'The Rexcelsior!' from The Lego Movie 2. Anyone shopping in a physical Lego shop will also get a free astronaut and satellite if they spend over £35 on anything from the Lego City range.
This kind of offer doesn't happen very often, so make sure you don't miss out. These things are currently going for £30+ on eBay.