Raised toilet seat

our pan opening of 36cm by 31cm is indeed larger than standard, so many raised seats will not fit properly. However, you have several good solutions:
Option 1 — Free-standing frame style (Best for non-standard pans)
These do not sit inside the bowl at all — they stand on the floor around the toilet, so they fit any size or shape of pan. This is the most reliable solution for your situation.
Aidapt Height Adjustable Raised Toilet Seat and Frame — fits any toilet, adjustable width and height, gives exactly 4 inches of lift
KMINA Toilet Frame / Safety Rails — free-standing, adjustable, provides extra stability as well as height
Maddak Tall-Ette or Homecraft Savannah — some models have wider base dimensions
Suppliers:
Mobility Smart — mobilitysmart.co.uk
Complete Care Shop — completecareshop.co.uk
Essential Aids — essentialaids.com
Living Made Easy — livingmadeeasy.org.uk
NRS Healthcare — nrscare.co.uk
Option 2 — Wider base raised seats
Some seats have larger internal apertures:
Big John Bariatric Seat — has an exceptionally large opening and fits most pans, available from Living Made Easy and Gordon Ellis & Co
Croydex Raised Seat — external width 365mm, may be suitable — check the internal aperture dimensions before ordering
Option 3 — Measure and confirm
Before ordering any seat that sits onto the pan, measure:
Internal width and length of the aperture
Distance between the fixing holes
Overall external width and length of the pan
Then phone the supplier's customer service with your measurements — they can tell you immediately if a specific model will fit. All the suppliers listed above are very experienced with unusual pans and will advise you honestly.
Option 4 — Replace the toilet seat itself
If you eventually replace the toilet, you can buy a standard-height pan and fit a standard 4-inch raised seat — which are widely available from all the suppliers above from around £25 to £45.

Yes — the keyword to search is “bariatric” or “super-sized” raised toilet seat, not just “raised toilet seat.”

Your opening is 36 cm x 31 cm, which is larger than many standard clip-on raisers. For example, one common 4-inch model from Aidapt lists an aperture of 265 x 209 mm, which is much smaller than your opening. That is why many ordinary raised seats are not a good fit.

The vendors I’d try first in the UK are:

Essential Aids — they list a Bariatric Super Sized Toilet Seat, which is the sort of product category that sounds closest to what you need.
Complete Care Shop — they stock several 4-inch raised seats and wider-access daily living products, so they are worth contacting with your exact pan dimensions.
CareCo — they carry multiple 4-inch raised toilet seats and may be able to advise on compatibility or alternatives if your WC is oversized.
NRS Healthcare — they are a solid mobility supplier, though at least one of their listed clip-on seats has a much smaller aperture than yours, so you would need to confirm dimensions before ordering.

My honest view: with a WC opening that large, a standard 4-inch clip-on raised seat may not be the best answer. You may be better off with either:

a bariatric / super-sized raised seat, or
a toilet frame / commode-style surround with seat riser, which avoids the fit problem altogether.

That matters because even if a standard raiser clips on, it may feel unstable or overhang badly on a non-standard pan.

I would contact Essential Aids or Complete Care Shop first and give them these three measurements:

maximum pan width
pan opening length and width
distance between seat fixing holes

Then ask specifically for a 4-inch bariatric or extra-wide raised toilet seat compatible with an oversized WC.

If you want, I can look for a few exact models with published dimensions closest to your measurements.

For a large water closet like yours (36?×?31?cm), standard raised toilet seats may not fit perfectly. The best solution is usually a frame-mounted raised toilet seat or a seat with adjustable/removable brackets, as these can accommodate non-standard bowl shapes and sizes.

When raising the seat by around 4 inches (10?cm):
• Make sure the seat is securely fixed and stable to prevent movement.
• Consider a model with removable or padded armrests if extra support is needed.
• Check the weight rating and material to ensure durability.

Vendors in the UK that supply wide or adjustable raised toilet seats include:
• CareCo – Pride Raised Toilet Seat 4?, adjustable fit
• Aidapt / Homecraft – wide range of adjustable or frame-mounted seats
• Gordon Ellis / Essential Aids – adjustable brackets for larger openings

If a standard product still doesn’t fit, a custom frame-mounted riser can be made to fit your specific dimensions safely.

Manage At Home: Stocks several specialist seats designed for larger toilets, including the Etac My-Loo, which is noted for its extra-large opening and easy-to-install bracket system.

CareCo

For non-standard toilet openings, look for universal-fit raised toilet seats and consider brands like Helping Hand or Ashby Lift that offer specialized models, such as the Ashby Wide Access Raised Toilet Seat from

Since your WC has a non-standard opening, standard raised toilet seats may not fit securely. We suggest looking at adjustable options such as the Ross Care Foam-Padded Raised Seat or the Mobility Genie Serenity Seat, both available in 4? height and designed to adapt to different bowl sizes