I know this is an old thread, but I'm surprised there hasn't been any mention of proper yeast rehydration when using dry yeast or proper pitching rates.
You will see a big difference with dry yeast if you do proper rehydration before pitching into your wort.
I know most of the dry packets say you can just dump them right into the wort, but if you do that probably about 50% of the live yeast in the packet will die off right away. If you take the time to properly rehydrate before pitching, you can get near double the amount of active healthy cells going in your beer.
I find with the Muntons this can be especially important because one packet already is half the size of a packet of Safale yeast.
Best bet is to just follow the yeast brand's instructions on their web site for what the proper rehydration process is.
The key is to put the yeast in the right kind of liquid to rehydrate. You don't want it to go dry into beer wort or into distilled/DI/RO water. You want it to rehydrate into clean sterile water, but water that is not as void of minerals, etc as distilled/DI/RO water.
The reason behind this is that when yeast is in the dehydrated form, its cell membrane becomes very weak. When it is first put back into a liquid, it cannot control what goes in our out of the cell membrane.
So, if it goes directly into wort, too much sugar and other stuff goes into the cell and it dies. If it goes directly into distilled/DI/RO water, the water is so pure that too much good stuff is pulled out of the yeast cell and into the water.
A good bet is to use dechlored, boiled then cooled (to sanitize) tap water. I've heard bottled spring water is probably okay, too, but may not be sterile directly out of the jug.
Also, proper pitching rates are important. The Muntons dry pack is half the size in grams of a Safale pack, so if you are going by packet count and not grams, you'll definitely have a difference in one pack of Muntons vs. one pack of Safale.
I like the pitching rate calc on mrmalty.com to determine how much dry yeast to use. I don't usually measure out to the exact gram, but at least try to get close with how many packs I pitch. The yeast amount calculated on that site assumes proper rehydration, so you may want to double the number if you don't rehydrate -- but then you're putting lots of dead yeast into your beer -- yuk!
Cheers and happy brewing!