Not sure what you mean by this. The issue is that currently welfare payments are earmarked: this money can only be used for rent, this money can only be used for food, etc. By eliminating our existing welfare programs, as is the case with every UBI proposal, we would instead be giving a single check and saying "manage this money wisely and pay your expenses." The problem is that when the money isn't earmarked for a specific purpose you can't be sure that the basic necessities are actually paid for before the money runs out. Just ignoring the fraud angle (spend all the money and claim an emergency makes you unable to pay for rent), how do you deal with someone having a _real_ emergency, having to spend all their UBI, and then being unable to pay for rent? Tell them tough shit? That's not what's going to happen.
I mean this is often not the case in the UK. We don't have food stamps and housing benefit is afaik generally paid directly to the person, not the landlord.
That's what happens now, whether the person gets money from a job or from any kind of benefits. Why should it change? It's called 'Basic Income', not 'Basic Relax All Your Needs Will Be Met'.
In the UK, many welfare payments go directly to the person, so this wouldn't be a new issue.
Many of them are designed really just to ensure a floor people don't drop below, but combined with exceptionally high marginal tax rates and odd conditions. The marginal tax rate in many cases is 100%, and can be above this.