"…has been towed away' is present perfect passive. That is why there is a 'been'.
Passive is formed with 'be' + past participle of the verb. Here the tense is present perfect so the present perfect of 'be' is needed - 'has/have been'.
It is passive because someone (we don't know who) has towed it away.
If you make it active, 'My shopping basket on wheels has towed away', it means that your basket towed something, and you need an object, e.g. has towed away my dog!