Many companies charge more for not paying by direct debit.
BT is £1.50 per month. Sky is £4 per month for TV. Virgin is £5 per month.
Some providers won't allow you to pay by any other means.
People don't seem to comment on Gas & Electricity providers though, maybe because they like BT until recently hid the extra charges in with the cost.
For example previously:
BT Charged £12 for line rental, but gave a £1 discount for paying by direct debit, now people have been happily paying this for years after years after years, as soon as BT drop the line rental down to £11, but then highlight a charge for not paying by direct debit (and increasing the charge by 50p) people complain. Crazy thing is BT could have simply increased line rental to £12.50 and offered a £1.50 discount for paying by direct debit and people wouldn't have thought much about it, even though it amounts to the same thing.
Now take gas and electric.
Pay your bill by cash / cheque when the bill comes and you pay over £200 per year more than you would if you paid monthly by direct debit. That's over a £16.50 per month charge for not paying by direct debit.
There is no real reason though why people shouldn't opt for direct debit, other than them being useless at budgeting and money management or living beyond their means if they are always running their bank accounts close to £0. maybe time to get rid of services and cut back on spending until you get to a point where you have several hundred pound buffer in your account and keep that there, just in case you need it if you ever lose a job etc or something breaks down, also don't borrow money you can't pay back if your circumstances change.
You can set up to pay your BT bill by direct debit, but a few days before the payment is meant to be taken you pay the bill, many people have been doing this, so they get the 'DD discount' but still pay the way they want. How long it will be before BT stop this I don't know, but people have been doing it for months.