I'd go over the top of Bournemouth then intersect a course which runs under N866 (or whatever it is now) to ORTAC (50 deg N). Bournemouth zone transits are usually no problem via the overhead "not above 2000".
If you want to go higher, call Plymouth Ops (number on the chart - look by D026) and ask them is the DA's are hot or cold. Often weekends they are cold, and often during the week too. Then you could take the recommended VFR route up to 10,000'.
When you are 10 miles North of 50N you will get handed over / told to contact Jersey Zone who will clear you in SVFR. They often give you vectors so I'd plan a route direct to JSY.
Another good route route if the DA south of Portland is inactive, is straight down over Portland, direct to ORTAC or 50N (I like ORTAC as it is in the GPS and you normally get asked an Estimate for 50N) but if you are at any altitiude remember you'll have to decend to 3000' to get below N866 (or whatever) nearer ORTAC.....