wordsmith, IME it's the cost rather than the lack of childcare options that's the real problem in my area. If you can afford to pay for childcare, you are fine.
I work full time but have flexihours and get enough leave to cover roughly 2/3 of the annual school holidays.
For the remainder I do the following:
Use playclubs - IME they cost about £12 - 15.00 for a 9 - 5 -ish day. You can book odd days at many of them and IME there is no shortage of spaces, even if you book last minute, though you might not get your first choice. The clubs prefer you to book way in advance, obviously so if they tell you places fill up quickly, take this with a pinch of salt. My sons at age 5 onwards really enjoyed them. I find it's the oldest one (age 10) who is less keen now, as the activities seem baby-ish to him.
You have one big advantage - as you work from home, presumably you don't need playcubs that offer extended hours ie 8.00 an to 6.00 pm. This will cut down the cost. One playclub I use charges £25.00 for a whole week (a 10.00 - 4.00 day). If I want 8.00 - 6.00, they charge an extra £25.00.
Go to your council for playclub info, but make sure they give you info for non council run playclubs as well as council run ones. IME the costs are often the same and it's important to know the full choice. Private run clubs will also include drama, dance or sports clubs.
HOwever, these hobby type clubs might not fit your needs at the moment. You may find your ds, at age 5, is still too young for many of them. Also the hours will be less. Typically, a sports session for younger children will last 2 or 3 hours only.
I agree with KS about childminders - again ask the council for a list of registered ones in your area. Many childminders don't work in the school holidays, but some do, and if you work non office hours, they can offer a tailor made form of childcare.
HTH