No.
Quoted directly from the Brooks of England website: "Proofide should be used several times during the ‘breaking-in’ period and every 3-6 months thereafter."

Proofide is a leather conditioner, similar in composition to Obenauf's LP (the only other product I suggest). It doesn't fully waterproof, but it does provide a degree of splash protection from light showers and under-saddle tire spray. While I'm a fan of most VO products, I don't recommend their saddle dressing. Silicone oils, similar to petroleum distillate oils reduce the breathability of the leather as well as damage the fiber structure. Stick with a compound like Obenauf's or Proofide and if you want to truly waterproof the thing just use a saddle cover. I like the Velox cover, and for $8.00 it's tough to go wrong; I've had mine for 4 years and it's lasted year-round commuting in the PNW, plus year-round randonneuring in the snow/rain. But if $8.00 is too pricey to protect your investment in a Brooks saddle, you can always go the shower cap route (about $1.00 at the corner drugstore) or a plastic bag (free with the purchase of groceries.)