The other tribal vote that most people won't talk about for fear of being labelled a racist bigot is the religio-ethnic vote or, to be more accurate, the Ummah vote. If nominating a corpse with a party rosette on would help to discover the base-line tribal vote for a political party, nominating a fictional candidate with the name Muhammed Hussain has got to be worth a try.
Based on my limited experience here in Bradford East, I reckon the base-line Ummah vote has got to be worth at least 300 votes for an Independent and a couple of 1000 for a party politician.
It does work the other way too, to a smaller degree. A number of people told me they wouldn't be voting for a candidate because they didn't have an Anglo-Saxon sounding name. No doubt those people would be labelled racist bigots, whereas voting for someone because of their Arabic sounding name wouldn't be!
I wonder what would happen if Harriet Harm-man's equality & diversity legislation was applied to voters! Imagine if you weren't allowed to discriminate on grounds of party, or race, or religion or sexuality before casting your vote!
First lesson in trying to get elected: Find yourself a tribe!