There's an old habit in this trade. Tenant looks a bit borderline on paper, so you ask for six months up front. Big lump in the bank, you sleep easier, everyone moves on. If that's still your plan, stop.
Under the Renters' Rights Act, once a tenancy has begun you cannot ask for, or accept, more than one month's rent in advance. Not three, not six. One. Take more and you are in breach, however willingly the tenant offered it.
I get why landlords leaned on it. A lump up front felt like a cushion against arrears. But the law now treats a big advance as a barrier that prices out honest tenants, and it's closed the door on it. So the cushion is gone, and the question becomes what you use instead.
Here's how I'd handle a weaker applicant now:
Reference properly. Not a quick glance at a payslip, a real check on income, history and any past arrears. This is where you catch the problem, not at the bank.
Lean on a guarantor. A named guarantor who passes referencing is now worth far more than a fat upfront payment, and it's fully allowed.
Keep the deposit clean. One tenancy, one deposit, protected on time. Don't try to dress up extra rent as a deposit to get round the cap, because that's the same breach wearing a different hat.
One more change worth your time: pets. You can no longer say no to a pet by reflex. You have to reasonably consider the request, and a flat refusal with no thought behind it won't hold. That doesn't mean you're defenceless. Ask for the right pet insurance or cover for cleaning, put it in writing, and consider each animal on its merits. A quiet older cat is not a young husky in a top-floor flat, and "reasonable" lets you say so.
From my own portfolio: I've stopped thinking of an upfront lump as protection, because it isn't one any more. The protection now is at the front door: who I let in, how well I referenced them, and whether there's a solid guarantor behind them. Get that right and you never need the lump. Get it wrong and no amount of advance rent saves you.
The takeaway: one month's rent in advance, maximum. Reference hard, use guarantors, and consider pet requests properly instead of refusing on instinct. The safety net moved from the bank balance to the vetting, so put your effort there.
If a landlord you know is still asking for six months up front, forward this before it lands them in trouble.