Substitute for British Golden Promise

I’m planning on brewing the NB Spiced Winter Ale. It calls for 9 lbs. British Golden Promise and 1 lbs English Medium Crystal. My LHBS doesn’t sell British Golden Promise. Can I substitute Maris Otter? And if so should I add anything else or is Maris Otter close enough?

Maris Otter is close enough especially for a spiced ale.

1+

My friend did that kit a year ago or so, from what i remember, the mulling spices will dominate any finer points the malt can contribute.

I agree with the above the spices will dominate any subtle malt flavor that GP produces.
So Marris otter is what I would use without a doubt. I also wonder what they gain by using GP
in this particular recipe as it is usually slightly lighter in body than MO.

Sorry to go somewhat off topic,
I typically dont like to be the one correcting ones pronunciation, or thought of a topic etc…but to set the record straight Golden Promise is Scottish. The only reason I know this is because most British ales excel with Marris otter, optic etc… But if you haven’t made the Innkeeper kit which is version of Timothy Taylors Landlord ale from Yorkshire. The Golden promise makes the difference. Also the best yeast to use with the kit is Wyeast 1469 Timothy Taylors strain( which is in stock at LHBS this quarter!). Also I have found when 1469 was not in stock or in supply at my place I have used British II and it was awesome as well.
Rant off, back to your normal beer discussion.