Sure that's possible. You will need a reservation for at least the Eurostar to London but the Interrail pass is enough as a ticket.

It is cotswolds. YOU/du also need to pay extra-and this can only be done (oh dear, the fear of all Germans) by simply holding cr-cd to turnstile for LON Underground-to reach the other station in LON. Or walk between these LON stations. However, even now after main season, it is very wise to REServe seats on this €* asap.

You may find the link useful.

https://www.gocotswolds.co.uk/blog/cotswolds-by-train-from-london/

apologies for the attached advertising for the tour company - I have nothing to do with them but first bit is relevant.

This trip is certainly possible, but I would recommend that you do your research and planning in advance. We have a general informational page for interested Interrailers here. Please note that certain trains in this journey, such as the Eurostar will require a reservation. The train system in Germany is likely familiar to you, but you can read about traveling in the UK by train here. Reservations in the UK are generally not needed, but it is important to note that they do not share their complete timetable data with us. You can find this directly on National Rail's website and add the journey manually to your rail planner app. You're welcome to ask further questions in the Community or you can submit a request to our customer service here: https://eurail.zendesk.com/hc/en-001/requests/new