I know that 0845 numbers are charged the same as geographic numbers from land lines but can't remember whether it's the same for 0870.Also what is the situation from mobiles.
By the way when I went to renew my BT phone contract they said that calls to mobiles are now the same as calls to landlines.

It is calls to 03 numbers that are charged on the same basis as calls to 01 and 02 numbers and included in allowances in the same way as 01 and 02 numbers.

All 084 and 087 numbers are premium rate with an Access Charge and a Service Charge. The premium is the additional Service Charge. These numbers are not usually included in allowances thus making them far more expensive to call than 01, 02 and 03 numbers. Calls to 0845 and 0870 numbers haven't been charged at similar rates to calling an 01 or 02 number since before 2004.

A diminishing number of landline providers still include calls to 0845 and/or 0870 numbers in allowances. BT is one of those that still does. Anyone that has inclusive calls to 0845 and/or 0870 numbers already has inclusive calls to 01, 02 and 03 numbers.

Most landline providers and all mobile providers include calls to UK mobile numbers in allowances on the same basis as calls to UK landline numbers. BT has only recently started to do so. They were the last major provider to do so. They do this only on the new price plans introduced in the last few months.

See also
https://planet-numbers.co.uk/news/uk-telephone-number-call-costs-guide/
https://planet-numbers.co.uk/about/cost-to-call/
https://www.ofcom.org.uk/phones-telecoms-and-internet/advice-for-consumers/costs-and-billing/how-much-does-a-phone-call-really-cost