I bought the Panasonic DMR-PWT550EB 4Kplayer thinking that it would play 4K discs when available. They are on the shelves now at £25. I bought one and the player will not read the disc.
Apparently Panasonic has just brought out the DMP-UB900 that will play the 4K disks. I think I have been conned.
I know I can stream 4K but I am not prepared to join the film channels.

Reject it then.

It's not a 4k Blueray disc player according to the website.

Only 4k networking and upscaling.

Not too sure how you feel conned, on the box it says Blu-ray/DVD Player & HDD Recorder and on the side of the box says 4K Ultra HD Upscaling.
Unless someone specifically told you it would play UHD discs then I'm afraid you made the wrong assumption.

On what grounds?

Unless the seller has misrepresented the item, then there are pretty much no grounds for rejection, though distance selling regs apply for a short time if bought on line.

They might get a good will gesture if they can show they honestly thought it was a 4k disc player.

TBH I think they should have a sticker on it, saying 'NOT A 4K Disc Player'

Thanks for the info. I can see now that it was my fault. It clearly says on the operating instruction book that it is a blue ray disk player.
It had just arrived in stock eleven months ago when I bought it. The assistant did not con me, he did say I could download 4k. I made the mistake of thinking the machine would be capable of playing 4k when the disks were available.
I had a similar experience when buying an HD ready TV and when the service started the bit was missing.
Hey Ho, Anybody want extreme Nature collection disc for the postage?

The OP implied he was sold a 4K player. Subsequent posts revealed this was not the case so no grounds after all.

i have a panny blu ray player. Dont like blu ray discs myself. They still look grainy to me. There is too much contrast , i have to adjust tv settings . I stick to ordinary dvds, Maybe 4k uhd ones will be better

Never had a problem with contrast on blue-ray, the grainy looks is sometimes the way films are made, some have a grain effect to make it look like film, but I do not see why they do that.

There was no implication in the OP at all. it clearly stated that he thought it would play 4K Blu-Ray discs not that he was told that or had it implied to him.
We know you hate Panasonic but that was just reaching at straws.

IIRC film grain was one of the most common early complaints about Blu-ray when people started to buy players and discs. Part of it was the extra resolution of BD which allowed detail such as grain to be seen. DVD wouldn't show anything unless it was really very prevalant in the transfer.

A lot of the time though it was (and probably still is) a case of having the TV sharpness control set too high. All the sharpness control does on its positive settings is to add noise to the picture.

Those directors still shooting with film today may make choices about film stock that is grainy for artistic or technical reasons. For example, indoor shoots in period buildings may be resticted about how much extra light can be used. Higher sensitivity film stock may exhibit more visible grain.

I can't say I've ever had an issue with excessive contrast though with a properly adjusted player and TV.