What was the capital city of England before London?

Winchester.
In 1519 Winchester was chosen as the capital of the kingdom of Wessex; and in 827, Egbert the first king of all England was crowned here. It then remained the capital and the most important city in England until the eleventh century and the arrival of William the Conqueror. He had himself crowned in both London and Winchester, and declared both cities to be capitals. However, by the fourteenth century the city had lost its place as the second most important city and began to evolve into what it is today - a small, sleepy, provincial city.
Ref: http://www.anglik.net/winchester.htm

With respect, 1519 doesn't make sense.

It replaced Dorchester (-on-Thames) as the capital of Wessex in 686 according to Wikipedia https://en.wikipedia.org/wiki/Winchester or 590 according to http://www.eupedia.com/england/winchester.shtml
Capitals were rather changeable in those days - the Royal Court being wherever the King happened to be. The capital was the place where he was most likely to be found. With the later increase of the civil service, the King's presence was less necessary and a fixed location for the administration more necessary.

I agree with Bloomsby: 1519 makes no sense.

I quote my Merrian Webster's Geographical Dictionary:
"Winchester was the capital of Wessex and the seat of government under Alfred the Great. It remained important under the Norman kings until the emergence of London as the sole capital of England in the late 12th century."

Don't worry about the 1519--it's a simple typo on the page Markswood copied and pasted from. The following is correct:

"The town has historic importance as the capital of the ancient kingdom of Wessex from 519."
http://1066.co.nz/Mosaic%20DVD/whoswho/text/Winchester%5B1%5D.htm