Jesus wept.
It's perfectly simple - unlike your incoherent and illiterate gibberish there. Portslade is part of the conurbation of Brighton & Hove - f*** knows why you keep saying it isn't. The fact that the name of the conurbation does not contain the word 'Portslade' does not follow that it is not part of it.
House prices have absolutely f*** ALL to do with determining whether a given area is part of a city or not. None.
It's you - and only you that's come up with the hair-brained rule.
All part of the Brighton/Worthing/Littlehampton conurbation.