This is a straightforward deal for families looking to get to London next summer without burning through their miles balance. At 40,000 miles one-way in economy, you're paying well under the usual 60,000-mile rate United often charges for transatlantic flights, and the $6 tax bill is refreshingly low compared to what you'd see booking through some partner programs.
Availability appears to be wide open for July 16, 2026, which is notable given that mid-July sits squarely in peak summer travel season. Finding award space to Europe during school holidays can be challenging, so this is worth a look if your dates have any flexibility around that window.
One practical tip: if you're booking for a family, search for all passengers at once rather than one at a time. United's award search will only show availability if there are enough seats for your entire party, which saves you from the frustration of booking one ticket only to find the rest of your family locked out.
How to book
Search and book directly through United's award search tool at https://www.united.com/en/us/book-flight/united-awards/search. You'll need a United MileagePlus account with sufficient miles to complete the booking.