This is a solid option for families planning a spring trip to the UK. At 40,000 miles one-way in economy, you're looking at a meaningful discount compared to the usual 60,000-mile pricing United typically charges for transatlantic flights. The $6 tax figure is also notably low for flights into London, which often carry heavier surcharges.
Availability appears wide open for April 3, 2026, so you shouldn't have trouble booking multiple seats together if you're traveling as a family. That's often the harder part of award travel planning, so take advantage while the inventory is there.
One practical tip: if your plans aren't fully set, remember that United allows free cancellation on award tickets up to 30 days before departure for MileagePlus members. That gives you some flexibility to lock in this rate now and adjust later if needed.
How to book
Search and book directly through United's award search tool: https://www.united.com/en/us/book-flight/united-awards/search