Congratulations Ed, it's a very nice knife. Harrison Brothers & Howson were a quality firm, and I did a lengthy write-up on them a few weeks back, with some photos of their Alpha Works, which still stands today. There has never been any legal requirement here to mark the country of origin on exported goods, and the addition or lack of an 'England' stamp would only be a factor on goods, knives in this case, specifically manufactured for export to the USA. Many post 1890 Sheffield knives, and even knives made there in recent times, lack a country of origin. That said, I don't think that knife is pre-1890, and my guess would be that it was produced many years later. Dating Sheffield knives is far from straightforward, but it's certainly a fine Lambsfoot specimen produced by a historic firm
Edit - Here's a
link to that recent post Ed