OK. If you want to make wheat flour tortillas (they are the typical Tex-mex tortilla beloved of US and British Mexican restaurants) you would be better strating from scratch.
You need 1kg of plain white flour, 2 tps of baking poweder, a pinch of salt ad 300g of lard (or vegetable oil), and a cup of hot water.
Mix the dry ingredients. Then add the melted lard or oil and mix, then add water bit by bit until you make a dough like ball. Take golf ball sized bits and flatten into circles (you can get presses that make life easier, but you might need a specialist shop). Cook on a very hot skillet or something similar.
Tip: you know when to turn them when the hot air inside makes the tortilla rise inside to look like a tent.
Maize tortilla, the Mexican (not Tex-mex) staple is easier. You need 1 kg of maize flour, a pinch of salt and hot water.
Just add water to the dry ingredients bit by bit until you get a dough. Then follow the same instructions.
It's not diffiult, but there is definitely a knack to it. You first effort will probably be a bit of the thick side.
Failing that, at the bottom of my street in Mexico is a little old lady who sells masa (harina or maíz) at a very reasonable price. It might cost a bit on the sirfarre though
Yes, I forgot that maize flour (as opposed to the common-or-garden corn flour we use to cook with) wasn't readily available in the UK.
However, if you are going to go to the expense of buying it by mail order from London, you might want to see if they'll sell you a tortilla press as well. This will make shaping the tortillas ever so much easier. A top tip is to line the press with plastic (I use old washed plastic bags that I buy my fruit in) so avoid the masa sticking to the press.
Flour tortillas are also lovely homemade, btw. Much better than the tat they sell you in a restaurant or supermarket. The great advantage there is that plain white flour is not difficult to buy!