We did it in reverse, and then came back to London again.
DD3 did a full year of reception in England, then started P1 in Scotland. We found that (having done Y1 with DD1 & DD2) that P1 was much more like Y1. They sat at desks a lot of the time (never in YR in England), teachers were relatively very strict, etc. The main difference was that DD3 starting P1 able to read confidently, having been doing it for a year in YR. The P1 teacher couldn't get her head round that at all. (I'm still furious about that 5 years later!
). Obviously I don't know your DC, but do try not to worry about that aspect of it too much.
Because English schools don't have the flexibility with start dates that there is in Scotland, you may also find there is a broader range of age and ability within the classes here. (That was our experience, may not always be the case, and will depend upon the size of school) DD3 was in a class in Scotland with children born within a few weeks of her (composite) but here has a full range from September to August. The difference that makes was particularly marked in the lower years.
That said, I'd say in London you are likely to find teachers (and other pupils) more used to children coming in with different accents (or languages) and school experiences. DDs school back in London has had numerous children starting with no English at all. A Scottish accent is (in our experience) seen as "cute".
Try to get as much detail from the school as you can about how the day goes, and little rules like when they are allowed toilet and water breaks, or where they get the fruit at break, or whatever, and I'm sure it will be fine.