Do your BTEC, English Lit and Psychology.
You may think Photography will be fun, but there's nothing fun about getting rejected from all your prospective universities because of your subjects which has happened so many times to people I know. Photography's also a bit pointless.
Psychology is a bit of a grey area for Russell Group universities - it's never really on the preferred lists nor the blacklists, I imagine it depends on how competitive the course you're applying for is. But since you are eager to study it, you'll more than likely put the work in to it and it's better to come out with an A in Psychology than a B in a more typically respected subject like Geography.
The BTEC, Psychology and Photography combined would not make for a highly academic application. And despite what I said about the example of Psychology and English Lit, for any RG university a B in English is probably better than an A in Photography.