Your husband is British, I would truly recommend that you apply outland, it would take approximately 9 months for 1st stage approval and the open work permit. London office I believe is processing applications on average 4 to 6 months.
This means if you apply inland, it will take about 9 months before he gets first-stage approval and a work permit; whereas if he applies outland, he will get his PR in about 6 months.
The 'London office' means the Canadian High Commission in London, where all applications from the UK are processed.
When you apply inland, the sponsor and applicant both have to be in Canada for the duration of the processing, and the applications are sent to Vegreville (in Canada).
When you apply outland, a sponsor who is a Canadian citizen can be living anywhere, in Canada or not.
The applicant can also be in Canada or in his/her home country: 'inland' and 'outland' refer to where the application is processed, not where the applicant is. The applications are sent to Mississauga (in Canada), which processes the sponsor's application and then sends everything to the visa office you select (in your case, London).
Your husband can come visit you in Canada while the application is being processed. Citizens of the UK do not need a visa to visit, so he should have no trouble coming in for a visit or vacation.