A question of security in England

Theft and vandalism - Not in the places you listed, they are not big cities. Leaving anything valuable out of site is sensible anywhere.
Much more danger of you scraping the car along the stone walls if you go onto some of the narrower roads. Tourists are always doing this in Cornwall.

We've rented cars for our last two month-long May holidays in the UK (2013 & 2014) and never worried about this. We drove throughout the entire island.

Some suggestions, however:

Keep obvious tourist "signs" out of sight: guidebooks, maps, free-standing GPS.

Do: Toss a newspaper on the seat, folded. A cup/mug in the drink holder. A shopping bag from a local store is good for catching trash and holding snacks.

I'm sure other will have some suggestions, too!

HAVE FUN!!

Gerri, it doesn't sound like you have much to worry about, I would only add a Don't: Don't get out of the car and go rummaging through the no-longer-hidden-luggage in the boot. Have what you'll need in the passenger compartment before you arrive and park. Arrive looking like a day tripper.

All the comments are great advice and we also take the time to not park in tourist areas. We strive to park in near by residential areas or, if available, office building garages. Essentially we are removing ourselves from the prime zones of where thieves most likely seek their victims.

when we travel we often have a car, so there is always the problem of leaving valuables ( eg computer/ipad etc) in the car ( or even in a hotel room, without a safe) while you are out looking around. my solution is a pacsafe 'portable safe' ( its a wire mesh lined lockable bag) that keeps the most valuable things locked to a non removable fixture in the car or hotel room. it gives us some peace of mind. the rest of our other luggage is considered not worth protecting. you can only do so much.

On every trip to the UK we hire a car, never had a problem, didn't even think that there might be. Just use your common sense and you will be fine.

I would never say never because thieves live in every town but the places you mentioned are definitely not hotbeds for such a thing though it could happen. Cars get stolen too. Be sure to buy the best insurance the rental company has and that it covers having the car stolen. Take the usual precautions you would in a city- nothing in sight in the car, no purses in car, all windows up and car locked, and lock everything you won't be carrying on you in the trunk BEFORE getting to an attraction so you aren't seen putting it in and leaving the car. Thieves will know you are a tourist by indications on the car and will expect you to hide goodies in the trunk. This makes your rental more likely to be broken into than a local's.

Thank you all for your advice! I've really enjoyed some of your posts, taken note of the sensible, and had a good chuckle over some of your comments. The only place I'm a little leery of is Brighton. We wanted to make a brief stop just to see the Pavilion and am a little concerned about my laptop and luggage in the trunk.

Keith... do we just make your day sometimes???

You will most likely be fine. However, there will always be some level of risk in all areas of the UK of 'smash and grabs' as they are called here. I would recommend trying to avoid parking in any dodgy or remote looking areas while your luggage is in the boot.