If it were me, I'd rather use stewing steak as it tends to be fattier and tougher than a good roasting joint, and benefits more from the long cooking without becoming dry and tough.  I think you might well end up ruining a really nice roasting joint and have a dry and mediocre stew at the end of it.  However, someone else may tell me I'm wrong ...

Its a no no...roast beef is for roasting, when additioned to a stew/hot pot it will be like chewing on old slippers   

Whenever I cook stew (normally in the winter) I buy 2 to 3 kg of beef rump generally in one or two lumps and then cube it myself. The local beef here is on the tough side so I boil it with onions for 2 hours in gravy (after sealing) before adding the vegetables.

Should I be using another cut? The results are always tasty.

Cheers

Y

I am with the others save it for a roast !
What you need for a stew is a muscle that has had to do a decent amount of work !
It will have more flovour and a better texture for the stew .
( says the vegetarian  )

Beerforyorkie , never boil the meat as it will be as tough as an old boot !
Either braise or simmer it gently , I have a slow cooker so often cook a 'casserole' type dish for a long time at a low temperature . It always ends up ' soft as butter ' .