For the more adventurous....
If you are sensible, and are carrying (as you should be):
1. No form or ID or card that can identify you personally (i.e. nothing in your wallet !)
2. An unregistered Oyster card or other pre-paid transport ticket to get you home
3. A PAYG mobile that:
(a) you bought for cash
(b) have only ever topped up with vouchers you bought for cash
(c) you have never once used to make or receive calls or texts from any number to which you can be personally linked
(d) you have never once used to access any internet service to which you can be personally linked
(e) you never switch on until you are least a mile from your home address
then you might get away with giving Police false details...
TBH though, it's hard to see how it could be worth the risk of committing such a serious offence unless you were pretty sure the girls was under 18 or coerced, and even then it could well end up being an aggravating factor when the judge comes to pass sentence...
If you do decide to gamble and give false info, you'd better hope you stood up your fake identity properly:
They say "Name ?" you answer "James Baker"
They say "DOB ?" you answer "3rd Jan 1978"
They say "Current address ?" you answer "Flat 99, 100 High St, London XXX XXX"
OK, so they carry on talking to you while another officer makes a phone call...
* When they ask, "how long have you lived at Flat 99, etc." and you say "err, err, about 4 years" and they do a quick check of the Electoral Roll and someone else's name entirely is on it and they say "why is that ?", what do you say ?
* When they ask "who can I call to confirm the details you have just provided", what do you say ? That you are single, have no friends or family, no employer .... ? Or give them a mate's number and keep your fingers crossed ?
* In this stressful situation, after 10 mins of sweating, will you be able to remember that DOB ?
The point is, any copper with more than 5 minutes on the job will be assessing how you answer as well as what you answer... if they're not happy, a reason will be found to detain you until they can confirm who you really are. If that turns out to be someone other than who you claimed, then you're fucked...