The only direct route from the UK to Denmark is Immingham to Esbjerg with DFDS Seaways. Six crossings a week are available taking 18 1/2 hours.
Many drivers travelling to Poland prefer a simple Channel crossing (Dover - Calais, Dover - Dunkerque or Folkstone - Calais) but you can also take the ferry from Immingham to Cuxhaven in North Germany. Cuxhaven puts you just over 600 km from Szczecin in North West Poland. This is around a 5 1/2 hour drive.
As before, journeys to Latvia begin with a crossing to mainland Europe via the Channel. To reach Latvia, depending on driving requirements, there is a ferry from Stockholm to Riga once a day with a crossing time of 17 hours. This will require a combined travel ticket for both the ferry between Germany & Sweden and The Oresund Bridge.
The ferry route to Ventspils is ideal if you want to minimise driving time and are heading for Riga, with a driving time of only 2 hours 20 minutes.
The quickest ferry route to Lithuania from the UK is from Karlshamn in Sweden to Klaipeda with one ferry crossing a day taking around 14 hours. The best way to reach Sweden from the UK is via the Channel, a combined travel ticket for both the ferries between Germany & Denmark/Sweden and The Oresund Bridge. Klapideia is approximately 3 hours from the capital, Vilnius.
After crossing the Channel and reaching Sweden via the ferry / Orseund Bridge route, four crossings to Paldiski in Estonia from Kapellskar in Sweden (north of Stockholm) are available each week with a travel time of around 11 hours. Paldiski is ideally located to the west of Tallinn with a drive of under an hour.