My friend is a roofer, he is really good, and really helpful, he does not carry any overheads so is really cometitive price wise, he has been doing it for 15 years+. And is also a joiner.
Ring me on 07974 681045 if you want some further info, Al
If there is an existing brick arch or brick lintol, should be ok. Remove a couple of bricks from under the arch and feel to see if there is a metal band supporting the arch. Wait a couple of days to see if any cracking occurs above the arch on the chimney breast or if any of the pointing has become loose due to settlement.
On the whole it should be ok as it is was constructed that way years ago, and generally the brick infill is not structural, its just there to block the hole or hang a gas fire off and provide a flu.
Hope that helps, Al