Thank you both for your advice,

there is nothing obstructing the perlins in the middle they have been
renforced with additional lenghs of equal size at some piont bolted to
the existing ones and feed into the party walls they have also layed 4"
by 2" lenths of wood the intire length of the roof jioned in the middle
with bolts on top of the joists to stop the roof from splaying I have
been told I can replace these with metal strapping as this is done on
most houses instead of using wood as it is less obtrusive. I have
obtained some metal banding from b & Q and was going to use this as at
the moment there is no tension on any of the spans i.e there is 7 in
total they are attached to the roof batons i think that the name for
them.

so if I get this right I can put in new jiost raised above the old ones
and two addtional ons in the middle and attach a web of timber to creat
a floating floor.

If I was to go over comply with building regulations on this part of my
build what size would the beams need to be out of timber and should I
imbed then in the party walls or put them on jiost hangers ?