Very nice pictures and nice looking octopus, thanks for sharing!!!
Don't think it is a vulgaris though.
What shop did you get the octo from and any idea which wholesaler they use? That can go a long way in determining which species it is. I live in the UK too and have a fairly good idea of who gets in what. Getting a bimac or vulgaris is never easy here
Looks like a horridus complex octopus, perhaps aculeatus or similar species.
The more pics the better, keep them coming
The Octopus horridus species complex is a group (more than 10 species) of small octopuses found in tropical waters of Indian and central and western Pacific Oceans. These species have long arms with the front arms being the shortest.
Members of the horridus species complex are capable of severing an arm to use as a decoy for preditors - the arm continues writhing.
If Silas is O. aculeatus, then he's probably an adult.
You might want to search on TONMO.com and else where aculeatus - it's a very interesting octopus.