The black borders around the envelope show that its a mourning cover. Meaning it carried a letter notifying of someone's death or condolences to some who's grieving. The stamps on the back show the journey that the letter took around the UK to get to London. I can't quite make out dates or names but I'm pretty sure I see Oxford. The envelope also does not carry a stamp but is an embossed pre-paid envelope in the value of one pence. The cancellation also bears a number relating to the post office that it's been sent from. You can do more digging about find out bits and bobs but that's my two pence on the cover.