As someone who's never been interested in effect's with jumbo cards before I have a dumb question.

Would a small 4 card packet of jumbo cards fit inside the inside pocket of a suit jacket or would they have to be folded up ?

This can be solved by 1) measuring the width of your pocket, and 2) measuring the width of your jumbo cards. OR you could go get your jacket and cards and find out. IF the problem is that they don't fit, then you have three solutions: 1) don't do the trick, 2) do the trick with smaller cards, or 3) attach the jumbo cards to a banker's bill clip and let them hang outside your pocket but still inside your jacket AS IF they were in your pocket.

Source for banker's bill clips: https://www.amazon.com/ACCO-Brands-72045......00J05FNS

I haven't got the jumbo card's yet hence my question, with me asking the question first prevents me wasting my money on something that isn't practical but thanks for your time.
I was hoping that someone who has jumbo card's and wears a suit when working might be able to advise me.

Most jumbo cards are 5" x 7", so if your jacket pocket is 5" wide or wider, you are good to go. But the banker's clips will work with any size pocket.

Thanks Jim I'll have a look what my pocket measures and as you say the clip is another possibility 😊

Yes, they fit just fine. Have used the inside jacket pocket for jumbo cards whenever I do walk-around.

I just use my jumbo jacket for my jumbo card tricks. I also have a mini jacket for the mini card tricks.

It would also be a relatively inexpensive thing to go to a tailor and have them sew an extra pocket inside your jacket to whatever specs you want.

As I have posted elsewhere recently, I carry a small sports-type duffle bag that I will sometimes pretend to rummage thru and then "accidentally" pull out a jumbo/giant size deck at least partway ("Oops!"). Spectators will usually smile and go along with the gag. If simply producing the deck is all you are wanting to do, then I can recommend this method, as it appears natural and requires no special pocket or other preparation.