What you'll need
 

Tools

The most expensive tool will be the sewing machine. Forget the idea of using your domestic all fancy electronic sewing machine. It will not cope with four layers of leather. The way to go is to get an industrial sewing machine. Unfortunately they're very expensive even secondhand machines will cost at least 700 Euro. Another possibility is to go retro. I'm using my grandmothers pre-war Singer 66 with the BUD motor and a Pfaff 30 (both built about 1932). They're mechanically strong and simple, easier to maintain and to repair than an old Jaguar. The only stitch pattern you need is straight and forward.

There are special needles for leather: they have a cutting edge. For the machine you need the biggest size (100/16) and plenty of them. Expect to work your way through at least 10 of them. Get one pack of normal leather sewing needles as well. There are a few spots where it is easier to sew by hand. You also need upholsterer's needles for the front seat base. They are bent and allow to fix the jute to the frame.

Very important is accurate measuring. Leather is quite expensive and once cut or sewed there is no way of reusing it. Don't use any steel tape for measurements. It will scratch the surface of the leather. Use a non metal measuring tape which will not harm your leather. In addition a wooden ruler is a very useful tool. It should be 1 m long. My method of choice of marking leather is taylors chalk. Most brands are easy to remove and don't leave any stains even when used on the front of the leather. But check first on a piece of scrap.

Cranked taylor's scissors are very convenient for cutting leather. Get a good pair for leather, calico, etc. and a second cheap one for cutting templates and paper. As far as knives are concerned cutting quality of disposable blades is pretty much the same. Check which handle you prefer. Always remember that the blades should never be stressed sideways as they're very brittle. For trimming you don't need them very often. I used it mostly to dismantle the old seats. A good clean cut can salvage your Dunlopillo.

For fixing your seat covers to the frame you'll need a good quality stapler. Like with needles you can also buy staples with a sharp edge. As far a I can see you don't need a hammer for the S-Type interior but for other types of Jags you will. There are special trimming hammers which are magnetic and have a soft-metal face.

Last of all you should have some metal spring clips with rounded edges or clothes pegs. They are used to fix the seat covers to the frame for fitting.