How to get driving (paper) maps in the county of Dorset?

The Ordnance Survey do road maps, and the one you'd need is sheet 7 - South West England. Saying that, for actual navigation I'd always recommend a traditional road atlas (combined with, as AakashM says, a traffic-watching GPS to avoid the snarl-ups on the M5). You should be able to get one in any decent bookshop, or in most petrol stations or motorway services. I'd got for one of the "concise" ones that are a smaller size, as the big A3 size ones can be rather unwieldy. Something like this one from the AA, for example.

If you're sure you want paper maps, it's probably best to just get a UK road atlas. The UK isn't a very big country so they're not very expensive.

Paper road atlases designed for exactly this are usually pretty widely and cheaply available in the UK from stationers such as WH Smith or Waterstone's, or any of a number of independent local retailers. You could probably buy one in advance from your favourite online retailer to be delivered to your UK destination, ready for you. A nationwide atlas is likely to be perfectly workable and not that expensive (under GBP 10); I've usually only bothered with county-specific atlases (note, as another poster said, that the sites you're looking for are in Bristol, not Dorset) where I need fine detail of residential areas.

All that said, I wouldn't buy one and haven't in years. Waze is an excellent free GPS navigation application with crowdsourced traffic data and more up-to-date maps which will make your journey much smoother. If you're concerned about data charges, Google Maps is also excellent for satnav and can be used completely offline if you download maps in advance - it doesn't take much device space for a really quite large area, and I traveled round northern Scotland that way last year with almost no signal but excellent navigation.

Most bookshops sell paper maps - Waterstones is the big national chain, but local bookshops will sell them too.

You can also pick up 2-3 year old road atlases in many bargain bookshops (e.g. The Works) for about £2. It's probably cheaper than buying them online, given you'd have to pay postage too.

If you head to the local tourist information centre, they often have free maps within leaflets for either specific attractions, or a group of local places. Depending on what you're after, they may be sufficient in some cases. They certainly would be as a supplement to a national road atlas.

Just buy one of these,

https://www.amazon.co.uk/2018-Collins-Road-Atlas-Britain/dp/0008214557

I think those are still widely available in the UK.

• bookshops at the airport (when you arrive)?
• at petrol stations en route?
• certainly at large bookstores in cities.

I much prefer "real, old-fashioned" paper folding maps,

https://www.amazon.co.uk/Explorer-Purbeck-Dorchester-Weymouth-Swanage/dp/0319242544

but they're harder to find.

(Well, trivially available online - if you have time just buy one from amazon .co.uk and they'll post it to you in Oz.)

There's actually a famous map shop in London, if you're in London you should go .. stanfords.co.uk?

An option no one else has mentioned is to pop into a local Halfords, which is your one stop car/bike/cycle parts and motoring-related-tat superstore chain - the nearest one to Bridport is in Dorchester.

As an ex-Brit I'd vote for buying a cheap road atlas from a service station (or Halfords) when you land.

But, another option if you're in the Perth Metro W.A. and desperate to plan ahead is to try here:- http://www.chartandmapshop.com.au

It's a great shop to just browse in and should have what you're looking for.