CBL's analysis points out the S I here
http://www.legislation.gov.uk/uksi/2001/341/regulation/29/made
I had previously read 29 without realising its import
as far as S Is go - these are probably the most tedious
basically five days to apply to the register
and five days to allow for objections to the application
and add a bit
not sure how you vary an S I
needs at least one vote in each house
a one line act would require three in each ( cd be done )
each years finance bill ( = budget ) is voted into action at 5pm on the day by resolution and the act follows a few weeks later
and I dont see why they couldnt do that
( but I am not a parliamentarian )