There's lots of discussion on tires in other threads, which you should review, if you haven't already.  I'll throw in a few more comments.

Does your car have power steering?  If not, then stay with narrow tires.  It will make turning the wheel easier when parking.  These things are a real bear to turn if you are not rolling.  I have radials on my 1953 Hornet, and with that big 308 lump of iron sitting on the front wheels, it's a workout to turn the steering wheel at low or no speed (and I still do dumbbell curls with 40 lbs each). Bias ply tires are somewhat easier to turn than radials, but radials handle better, brake better, and stick to the road better.  

Which leads to a second question:  How do you plan to use the car?  Sunny days to go to local car events, or regular driving in all road conditions?  If the former, consider staying with bias ply tires.  Besides, they look more period-correct too.  If the latter, then get radials and put up with having to go back and forth several times to get in and out of a parking spot or your garage.  But I'd go with narrower tires. 

Thanks for your comments Peter. Now I have retired she is becoming a much more regular driver especially for out of town (around town the Essexs get used more).. I can't always take the modern as my wife needs something she can drive when she needs to! I dont do car shows as such but also a lot of car club runs. Garage parking is no issue and if in town I choose angle parks now anyway. I will give the 215 radials a go when the replacement time arrives and hope that I have made the best decision.

I checked my tires today. They are Cooper 225/75R15. They were put on by the PO, so whenever I replace them, I’m going narrower. I will note, however, that with those tires, my odometer has an error of less than 1%.  

The other thing that you can do to reduce steering wheel effort is to keep the air pressure high—30 psi or more. 

On my '51 Pacemaker Coupe I run 215x75R15 all season tires and never have had a problem.  I don't know the wheel width, but because of the history of the car I would be inclined to think 5"

For the record and for those who want to maximize filling the front fender wheel opening a 235/70 tire does fit. IMHO the stance of the car is enhanced as this gap between the top of the front tire and the horizontal fender line is decreased. HOWEVER there's no denying that installing and removing 235/70's from the rear axles is like pulling on a fat bear (as your frustration grows his anger hardens!). I run mine @32 -34psi and deflate the rears before removing (inflate them back up after install).    

Alistair, Hudson offered 5.5 wheels for convertibles and hrdtp's. These are realitively hard to come by. We use the 5" wheels all the time with good results.  Just remember to inspect the wheels for excessive rust, bends and/or wiggles.  Take the rims to your local tyre shop to have them check for trueness.  We also use 225/75/r15, and no bigger.  As pointed out here, 235/70 is too large to fit in the opening, and is too wide for the 5" wheel.  235 is the radial eqivelent to the "L" letter old series of tyres.  The radial profile is just too big, especially when trying to install on the rear !  Hope this helps.

Today I installed new 205/70 R15's (Hankook Kinergy ST H735) on the '54 SuperWasp.

The car is outfitted with the DG200 automatic transmission (due to the fire at the Hydramatic Plant in '54 ) and a 3.07 rear end. The DG200 is basically a two speed transmission with a large split between low and high gear (from 2.9 to 1).

In this case I opted for the smaller diameter tire to incrementally help the engine over come this large split at low speeds.  Even with the smaller tire when the tranny shifts from low into direct drive at 25 mph the engine rpms drop from 2850 rpm to 985 rpm! When cruising the freeway @ 65 mph the engine will jog along at 2560 rpm.

I expect the car will exhibit nice road manners and achieve good gas mileage on flat lands. But powering through steep long grades will be another story. Especially if/when speed threatens to fall below 42 mph = 1680 rpm i.e., where'd that torque go?, slam, surge, screaming 262 Wide Six @ 4200 rpm!   

(ps --installing the 205s was angel cake compared to 235s)