thick muffin batter

Today I tried a UK recipe for muffins for the first time. The main ingredients were 250g whole wheat flour, and a small amount of splenda for the dry and 150ml milk with one egg for the wet. This was the stiffest dough I've ever tried to stir. When I used to make muffins in the US it was a pourable batter. This was so stiff I had to double the milk before I could even attempt stirring in the blueberries. They turned out fine so I'm not sure if this was a typo in the recipe book or if muffin batter here is meant to be that stiff?

My mother in law made muffins this summer and her's was the same ( different recipe though) but she's not a baker so I assumed it was her not the recipe. :p

I cant offer any help here, as my muffins come straight from a box of ready made mix however that doesnt sound like the consistency they should be. even the muffins that I buy from the baker arent any stodgier than the ones back home, so youd think the batter couldnt be thicker? even scones which are basically biscuits, arent that stodgy in consistency? maybe try a different recipe,.
http://www.healthy-eating-made-easy.com/healthy-blueberry-muffin-recipe.html
http://www.elise.com/recipes/archives/001412blueberry_muffins.php
that last ones pictures looked soo yummy!

I've used this recipe twice with no problems

Makes about 12 muffins (UK notes here)

2 1/2 cups fresh blueberries (I used a 300 g package)
1/2 cup butter (115g)
2 cups flour (420g plain flour)
1 cup sugar (200g granulated sugar)
2 eggs
1/2 cup milk (120 ml)
2 tsp baking powder (not being able to find MIL's measuring spoons I used an actual teaspoon )
1/2 tsp salt (ditto)
1 tsp vanilla extract (ditto)
2 tbsp sugar for tops (I sprinkled an unknown amnount of granulated sugar)

At low speed cream the butter and sugar together. Add the eggs one at a time. Mix and sift the dry ingredients and add, along with the milk. add vanilla(the batter seemed too thick at this point so I added a splash more of milk). Stir in berries by hand. Pour into greased muffin cups and sprinkle sugar on top. Bake at 350 F (approximately 176 C) for half an hour and let cool in the pan. (I found I needed to go around the edges with a knife to get them to come out of the pan).