Source of balloons:

http://www.evertsballoon.co.uk/product_giant.html

A friend used the 1m dia balloons to hold up a 5/8 on 80m. He got
about two weekends out of a balloon, but I think that a top-up
may have been needed on the second weekend.

The Air Navigation Order

http://www.legislation.hmso.gov.uk/si/si2000/20001562.htm

makes interesting reading. Provide you confine yourself to small balloons
which are defined as:

'Small balloon' means a balloon not exceeding 2 metres in any
linear dimension at any stage of its flight, including any basket
or other equipment attached to the balloon

... you have quite a lot of freedom.

It is not clear whether the teather counts as part of the balloon or not.

73

Stewart G3YSX