HMRC will see both the income and the outgoings, maintenance costs etc as received and incurred 50:50 by you and yor brother, as the property is in joint names, despite who may actually pay for what or receive what income.
This is to avoid the situation where, for example, home owned in joint names by husband and wife, and rented out. Woman pays top rate tax (40%), man pays basic rate tax (20%). They prefer to say 'the income all goes to my husband, my husband pays all maintenance etc, all should be taxed on him at his marginal rate (20%)'. Even though this is actually the arrangement they have, HMRC has specific guidelines for this scenario, and their take is that if a property is in joint names, all outgoings/income is deemed to be split 50:50, despite the fact this may not actually be the case. This blanket rule is to avoid a tax loophole.
In your situation, both you and your brother should declare 50% each of the total income, and claim 50% each of the maintenance costs. Hope the above is clear, if you call your local tax office they will be able to confirm.
One caveat would be that it may be possible to have it all taxed on you if you call HMRC, explain the situation, and request that under the circs they do not deem all the income and outgoings to be split equally, even though the ownership of the house is split equally, if this is what you would prefer to happen. Don't know what they'd say to that, but worth a go if that's the result you're after.