Which is the UK's biggest bird, native or otherwise?
My guess would be the Mute Swan, I can't think of anything bigger than that, bit I'm not 100% sure!
Mute swan was my answer until I put the question into Google and came up with
this. I hadn't heard of it before, but does it count?
I think this one takes some beating
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White-tailed Eagle taken last June in Mull
If you go for the otherwise, then it has to be Ostrich.

What about the Great Bustard?
I didn't think it would count because I knew they had been wiped out then I discovered they had been reintroduced here (see link below)
I spent a day looking for them in Portugal with no luck and had to settle for Imperial Eagle - thems the breaks.....
It sure is a big bird.
http://www.greatbustard.com/
SCR

Fastest: Whilst swooping to catch their prey, the Peregrine Falcon can reach speeds of approximately 120mph (200kph)
Largest: With a wingspan of 2-2.5m (6-8ft), the Mute Swan is Britain's largest bird and at 10-12kg (22-26lbs) the Mute Swan - Britain's heaviest bird - is also one of the heaviest flying birds in the world.
Smallest: The Goldcrest is the smallest bird in Britain with a wingspan of just 13-15 cm.
Oldest: The oldest bird ever recorded in Britain is a Manx Shearwater that was ringed in 2004 as having reached the grand old age of 52.
Most Travelled: The above Manx Shearwater is also thought to be the most travelled bird in Britain. It has been calculated that the bird may have clocked up more than five million miles during annual migrations to South America and regular 600-mile feeding trips throughout the year.
Largest Nest: The largest bird nest ever found in Britain belonged to a pair of Golden Eagles and measured more than 4.5 metres (15 feet) deep.
Greatbustard.com has the following to say:
Great Bustards were formerly very much part of British wildlife before they were finally hunted out of existence in Britain by the 1840s. They have suffered similar dramatic declines in numbers across their range in the last 200 years and their global population is now estimated to be just 35,000 individuals.
Marked difference in size between male and females, termed sexual size dimorphism. Great Bustards actually exhibit the largest sexual size dimorphism of any bird species and even most other vertebrates! Female Great Bustards can be as much as 50 % smaller than males.
Males: Standing height 90-105 cm. Wingspan 210-250 cm. Weight 8-16 kg but reports of over 20 kg make them the world’s heaviest flying bird!
Females: Standing height 75-85 cm. Wingspan 170-190 cm. Weight 3.5-5 kg.
So if you can count reintroductions they just pip the Mute Swan!

My guess would have been the mute swan, but a quick search led me to a site where the common crane is the tallest, while the mute swan is the heaviest. Fascinating!
I would think the Mute Swan was the largest native British bird
Mute Swan has the most feathers of any british bird.
Wow, I didn't know that! :O