You may be eligible for full or partial relief from CGT depending on your exact circumstances. I assume you lived in the house before you went abroad? If it's your only UK property and you have been away for work for less than four years, you will be eligible to full relief. Even if you have been away for less than that time you may still be eligible for partial relief.
There's some more detail here: https://www.gov.uk/tax-sell-home/absence-from-home
However, CGT rules are complex and this is an area where it would pay to get some personalised advice as any mistakes could be costly.
As for whether to hold or sell, it very much depends on the specific circumstances, and even then there's likely to be no single right answer. A few questions that would run through my mind:
1. Is there a mortgage on the property? If so, selling it will release the equity and reinvesting in equity markets will be an unleveraged return which will affect the relative returns between the two options.
2. Is it empty or tenanted? If you have sitting tenants then you have the security of a monthly rent cheque and they are covering liabilities such as council tax. In those circumstances I'd be inclined to hold on to the "bird in the hand" rather than chuck them out and move on.
3. Is the property located in a part of the country you might want to move back to in future? We all talk about UK property prices but in fact there are hundreds of different local markets moving up and down at different rates. London property is doing relatively less well at the moment, regional cities like Manchester and Birmingham much better. If the property you own is in an area that is different than the one you may want to move back to, it will not be a perfect hedge in any case.
4. As has already been pointed out, neither the FTSE 100 nor the 250 are particularly correlated to residential property markets. There are some individual stocks which are (housebuilders, "build to rent" landlords like Grainger plc) but even these face different risks and will not necessarily follow the property market exactly.
5. Selling up this property and moving to another (as suggested by the previous poster) would leave you paying a fair whack in Stamp Duty Land Tax. That doesn't necessarily make it the wrong thing to do, but it's a huge transaction cost you need to be aware of.
It's impossible to give any sort of advice without knowing the answers to some of these questions but I hope that's food for thought. In general though, if it's rented out to decent tenants and isn't causing you any hassle, I would be tempted to stick with it. If it's empty and you're struggling to maintain it from overseas then an equity investment of one sort or another would probably reduce the hassle factor and be easier to track and monitor.