Great Blue Heron Immature? (Hampshire)

We saw this in our garden yesterday (29/10/2020), and were curious as to what type of heron this is? 

Google suggested it might be a Great Blue Heron (Immature), but we're no experts and this bird is very rare in the UK. 

Whatever the case it was fabulous unexpected guest on a miserable afternoon (weather wise!). 

Please can anyone verify?  I have a few more photos.

Many thanks.