The nutrition information at http://www.tesco.com/groceries/Product/Details/?id=253907836
does not specify the moisture content of the Hovis Strong White Bread Flour so it is hard to convert the protein content of that flour to a wet basis to equate it with a U.S. protein value. However, if the protein content of the Hovis flour you are using is around 12%, you should be able to safely use 61% hydration, as you noted in your recipe.
The recipe you are using looks to be fine for a NY style dough. With respect to the amount of yeast (IDY) that you have been using, I think it is OK but since it appears that the temperatures in England are presently on the cool side this time of year (a range today of about 1-14 degrees C in London), it perhaps wouldn't hurt to increase the IDY by about 5-10%.
I also think that your general dough management is satisfactory. This leads me to suspect that your shaping and stretching skills may need more practice. As for videos, you might take a look at these:
(ignore the perforated disk part if you are using a pizza stone)
As kind of a crutch until you are able to gain the skills needed to shape, stretch and toss a dough base (if you would like to do that), you might try the method described by Tom Lehmann in his PMQ Think Tank post at http://thinktank.pmq.com/viewtopic.php?f=6&t=6410&hilit=#p41080.
If you'd like to see how that approach is sometimes used in a professional setting, watch this Lehmann/Zeak video:
How to Make Pizza Dough pt.3
Keep in mind, however, that professionals who specialize in the NY style do not use sheeters or presses and the like (or dough dockers). I just wanted to give you several perspectives on the matter of forming bases.