Jake Hi, I got my Butane torch elsewhere but "Maplins" do sell an almost identical item, It goes under the name of "Maplins 30 Watt Gas soldering iron kit" About £20,
As to holding the PE in place it depends totally on what your doing, often the PE is already attached to another part of the build but if you do need to clamp it together if you go to E-BAY and type "Small Plastic Clamps", There are some on offer at the moment "8" for £2 with freepost and Rad can probably get a truck load for 50 P,

Whatever,
Clamp, secure and generally hold together the Pieces of PE,
Carefully open the Solder Paint Pot and even more carefully stir the Paint with your Paint brush until the contents are of equal consistency,
Apply a coat of Solder paint along the Joint, Not too thick you are not painting a fence

and "Wipe" the Butane Torch across the Joint, You will see the solder run into the joint and Job Done,
It is worth spending a few minutes practicing on scrap work before doing the real work.
I like to have a strong light source over the work while I am soldering.
By the way if you use "Shrink fit tubing" for insulation on the wiring the butane torch is an ideal way to get the "Shrink" done
Shaun.