The fun is running very slow and it lead to overheating of this engine

Low on coolant? Often the cause of poor heater performance. Also a reason for overheating. Be careful, overheating can lead to expensive repairs, engine wise. I would not be driving the car until the overheating is solved.

If it's carburettor engine then you might have a speck of dirt or water in the idling jet. A quick way to clear it is to swap over 2 or 3 ht (spark plug) leads and let it backfire a bit. Just remember which leads you swapped over.......

If it was "steaming", "slowing down" and finally "quit running", it doesn't sound out of time to me! It sounds SEVERELY OVERHEATED. I would be checking the engine coolant level. If it is low (which it sounds like it most likely is) Then you need to find out where the coolant is leaking from. Maybe you will get lucky and the engine will not be totally destroyed.

Also check for engine coolant in the oil....If there is coolant in it, it will look like a chocolate milk shake. this is an indication of blown intake or head gaskets, cracked cylinder head and/or cracked/broken cylinder walls. (very likely on an overheated engine)

Converter is ruined, as are the O2 Sensors

Now you have to fine out why

Rich Condition or Overheating,
Engine Misfires

Have fun !!

Overheating can seriously damage a car's engine if left unchecked. Although overheating simply means that a car's engine temperature exceeds normal operating temperatures, the causes of overheating are varied. What follows is a brief list of some of the most common causes of engine overheating.

Faulty Radiator
1. A car that overheats will often have a faulty radiator. A radiator is responsible for cooling hot engine coolant that picks up heat from inside a car's running engine. A radiator "radiates" the heat from engine coolant out into the outside air. A faulty radiator loses its "radiating" effects and allows engine coolant to become overheated, thus rendering it ineffective at adequately cooling and engine.
Faulty Water Pump
2. A faulty or malfunctioning water pump prevents adequate engine coolant flow and can cause a car to overheat. A water pump serves to pressurize and propel engine coolant throughout a car's engine and radiator to increase the heat-reducing capabilities of engine coolant. A faulty water pump loses its ability to adequately pump and propel engine coolant, and can cause a car to overheat.
Coolant System Leaks
3. A leaky engine coolant system reduces the level of circulating engine coolant, which increases engine temperature and leads to engine overheating. Radiators, water pumps, and coolant system hoses and seals--all of these coolant system parts can develop leaks, which can result in low coolant levels and engine overheating.
Faulty Thermostat
4. A car thermostat regulates the flow of engine coolant. A thermostat is a heat-sensitive valve that opens when a car engine reaches a set operating temperature and closes when a car engine is cold and warming up. If a thermostat gets stuck in the closed position, coolant will be prevented from reaching the engine, which will quickly lead to engine overheating and potential engine damage.
Low Engine Oil Level
5. Engine oil, in addition to lubricating an engine's internal parts, helps to keep engine operating temperatures reduced by eliminating friction within the engine. If engine oil levels are low, friction and heat build up inside an engine, a condition that causes increased engine operating temperatures and can lead to engine overheating.

A constantly blinking check engine light means you have a misfiring engine that is bad enough to cause your catalytic converter to go bad! Take it to the shop... probably means ignition parts and the upper manifold has to come off... and that's no fun! Good luck.

Well at least its fun when it happens.

But seriously either the engine temp sensor or thermostat needs replacement.

Sounds like something is overheating then and possibly a sensor. Not familiar with Rovers but might be a problem with the CAS and/or CPS which tells the ECU the motor is running and when to fire. Also maybe the IAC is bad and when you go from throttle to idle it can't control it and allows it to die.

Are you quite sure it is not overheating? Your mention of heavy traffic, ie. stop and go, would tell me that your radiator fans are not working. I had a car with bum electric radiator fans. It worked fine if it was moving a lot. But in slow traffic, it would get warm enough to have a vapor lock or something without setting the engine-hot light.