Simple list problem that's defeating me!

[Neil Webster]

Hi all,

I've got a simple problem but it's defeated me and I was wondering if
somebody could point out where I'm going wrong or offer an alternative
solution to the problem?

I have a list of lists such as [[a,2,3,4],[b,10,11,12], [a,2,3,4]].  I
need to combine the two lists that have the same first character in
this example 'a'.  In reality there are 656 lists within the list.

My attempt so far is:
L = [[a,2,3,4],[b,10,11,12], [a,2,3,4]]
d = []
z = 1
while z <= len(L):
	for a in L:
		if L.count(a[0]) > 1:
			d.append(a[2:])

	summed = [sum(pair) for pair in zip(d[0], d[1])]
	z = z+1
	print summed

Any pointers more than welcome.

Thanks all.