IN your own country Interrail allows 2 trips: OUTbound and INbound-can also be to airport or seaport and do not even necessarily have to be 1st/ast day of use. On the new style app you are allowed even 2 traveldays IN own-but UK protects income-due to its skyhigh fares-and there are frequent reports that roundabout trips etc are not allowd.

Thus you fly out/in on other trips, use the bus or pay up for more trips on €*

Note that supplmt to use €* is 30€/ride and this is often more as the lowest full fare BUSticket to Par/Bru or whatever. There are also quota-if youre npot lucky its also full fare.

Hello, each pass only has one allocated outbound day to exit your country of residence and one inbound day to re-enter your country of residence. While you certainly can take additional trips to/from your home country, the pass won't be valid for this. You can purchase point-to-point full fare tickets for all additional journeys within your country of residence and then continue to use the pass once you've reached the border. I hope this helps! :) 

I am unsure what you mean by UK protects income due to its sky high fares. That is only the case for UK residents outside of the 2 IR days (and we well know the costs).

If you are an interrailer from outside the UK there are no worries and reservations are free.

If you are a resident in the UK with an IR pass you have the 2 days you can use the pass for unlimited journeys so again no fees for internal travel, irrespective of distance travelled or number of trains taken. 

Remember also that, although not in the spirit of IR, you could even use those 2 days for domestic journeys e.g. London to Inverness and back a few days later (£201 e/w for fully flexible ticket). Useful if, like me I live near a local airport and Hull ferry port, so do not use E* for my outbound/return days for my trips.  

As is clear in your post, on all other days of a pass a UK resident leaving or returning has to pay to their start point on the mainland or from their last IR point before entering the UK.

Also I am not sure what you call a roundabout ticket. Yes we have a complex system of operators and ticketing but with an IR pass you can make as many combinations as you require without concern  They are simply added as journeys.

For UK residents there are some mini local rail passes that allow freedom of journeys on circular routings, but that is all.