Call charge - unable to find in published tariff list

[#1]

I have a call charge itemised as follows:
Date of call  Number called  Time of call  Duration  Cost
11/03/2012 07513XXXXXX ** 20:11:25    00:01:00 £4.73
** Operator Assisted or Reverse Charge Call
I'm not disputing the call (though I don't recall it), what I am unable to do is confirm it as I cannot find any reference to this call type in the homephone tariff https://portal.plus.net/residential/tariffs/homephone.html
I do think £4.73 for a 1 minute call seems rather steep regardless of it being operator assisted or reverse charge.
Can anyone help me confirm that this charge is valid?

[#2]

However this BT charge sheet gives you the bad news http://www.bt.com/pricing/current/Inland_Operator_boo/2-1114_d0e1.htm for calls from pay phones
Operator service charge £1,99
Call charge £1.99 per 30 secs for the first 10 minutes
I can't find anything about reverse charge calls from mobiles but I assume the mobile phone company tariff would come into it and it wouldn't be much different

[#3]

Hi, I'm looking at our call tariffs to ensure that everything is included and I'll ensure that a note is added to show what extra costs may be incurred for an operator / reverse charge call. I'm not too sure at the moment what the exact pricing structure for these are, or if it's different for different call types (mobile, landlines, etc.) so I can't give any further information at this stage I'm afraid!

[#4]

Thanks for the replies.
I'd appreciate some kind of warning about the potential cost of things like reversed charge calls from mobile networks (is it the mobile operator that actually governs the charge for these?).  Are they / should they be allowed to charge this kind of amount without announcing the potential cost at the beginning of the call as this surely is premium rate territory.  We would not take any such calls if warned at the beginning of the call that it would cost a minimum of £4.73!
I'd imagine the call (logged as one minute exactly so almost certainly rounded) consisted of something like 'hello, it's me, can you call me back on 07....', I doubt if the call was actually any longer then 10 seconds (and was immediately followed by a 'normal' mobile rate call to the same number).