I was always taught that the word however is either surrounded by commas, in a sentence like If you do this, however, you will get into trouble, or else it must be either the first or last word in the sentence, and whatever its position, it is an adverb. Now, even on government websites, it is used as a conjunction in the middle of a sentence, with a single comma (sometimes before it, sometimes after) which clearly (to my ears at least) does not fit the intonation. Here is an example from the Highways Agency:
Depending on the stage of works it may be necessary to maintain lane or road closures, however we will do everything possible to open lanes as soon as we can.
Obviously no one proof reads anything any more (re-write: … road closures. However, we will …)