One of Australia's favourite holiday spots could soon cost more to visit

Australian families could be forking out hundreds of extra dollars to visit the UK due to a new tourist tax.

The UK government has passed legislation allowing British mayors to introduce a "modest" nightly tourist tax that would apply to overnight stays.

The levy will apply to paid accommodation for tourists such as in hotels, guesthouses, campsites and holiday letting platforms such as Airbnb.

The tax is set to be included in final accommodation bills as a separate charge.

All tourists, regardless of nationality, will have to pay it.

Early modelling suggests the fee is unlikely to exceed a few pounds - around £1-£2 (roughly AU$2-$4) per person per night.

For a two-week stay, that would be approximately AU$28-$56 per traveller.

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But couples or families would need to multiply that cost per person - which adds up quickly.

A family of two adults and two children holidaying in the UK for a fortnight would spend between AU$112-$224 on the levy alone.

For comparison, Edinburgh is set to introduce a levy of five per cent of the net accommodation cost, capped at five nights.

Wales plans to charge up to £1.30 (AU$2.60) per night.

The levy amount will be decided by each British mayor, meaning costs and rollout dates will vary from city to city.