Practices. "Practise" only when the word is a verb. That's UK usage. The commonest mistake in the UK is to use "practice" for everything. Dave Mallinson's Absolute Beginners manual used "practice" throughout and he apologised in the foreword, which had clearly been added post-proofreading.

Anyone who ever pronounces the h in honest or hour, and several others, is semi-literate at best. Both words when written require "an."