Big kit advice

Have you tried the non Pro Team Rapha kit? I have fairly simular sizing to you, 38" waist and a 44" chest. I go for the xxl bib shorts and an xl jersey. The xxl jersey should be good for a 46" chest. Pop in to a store and try it. 

Try Endura kit - that seems to come up huge. I'm normally a medium in most things, but even their small is big on me.

Pearl Izumi and other US brands might do better for tall and mighty sizes.

Not surprised most European brands come up small given your upper body measurements.

aerotech:

https://www.aerotechdesigns.com/?gclid=EAIaIQobChMI4KbqmMfI2AIVSbbACh1PQ...

They are based in Pittsburgh, Pennsylvania USA so shipping would probably take some time if they ship to UK at all.  I bought one size 4x vest from them and it is very well made.

Fat Lad will certainly fit your width, not sure about height but Richard the owner is a tall chap so they must have a jersey to fit you, give them a call. Prendas should fit you fine width-wise again. Both very nice quality clothing.

If you want to pay less then Funkier and Tenn outdoors do stuff for big and tall guys. Both brands' jerseys and bibs are ridiculously long on me so they should fit you.

JE James often have bigger sizes than other shops, worth a look.

Have you looked at the Fat Lad at the Back stuff? I've no experience of their products but they do larger sizes.

X2 for Prendas - Drop them a line and they will help you with sizing. Delivery is amazing - so fast it almost arrives yesterday!

Does it have to be cycling specific gear?

Personally I like to wear t-shirts made from sweat wicking material, I find them more comfortable, they're a fraction of the price, and I prefer the look. The choice in sizing should be far bigger, anything from skintight compression tops to baggy as you like. Should be plenty to choose from in sports shops, mountain warehouse stuff is decent value as well.

If you're going for the full cyclist look then it might not be the best option. 

i'm a fair lump..my castelli stuff is xxl or xxxl..my morvelo tops fit when i'm 10/15 pounds lighter in the summer, the prendas jerseys i've got are excellent and as others mention go to bigger sizes mine are 4xl and i wear them year round because they can accomodate a few pounds extra without me looking too much like a bursting sausage.. they are terrific folk to deal with too.

Prendas  - most of their Santini jerseys go up to 8X which is a 52" chest. Epic customer service too.

Or Fat Lad at the Back.

ive had some decent riding gear from cannondale, that fitted me fine, even managed to reach my wrists even with my gibbon like arms.

avoid anything italian, it will be too small.