Training for Competitions
There are a lot of national tournaments that can be entered into when climbing the ranks. Most of which are entered through local clubs.
Snowsport England (SSE)
This organisation body run a number of weekend rollerski cross-country ski courses for all levels. Further details: https://snowsportengland.org.uk (or ask at your local cross-country ski club).
This organisation body run rollerski cross-country ski courses for beginner and intermediate levels.
Further details: https://en-gb.facebook.com/snowsportscotland/ (or ask at your local cross-country ski club)
Cross-Country Ski Clubs
Most cross-country ski clubs provide cross-country ski lessons on rollerskis.
Snowsport England (SSE) run a week on-snow cross-country ski course (usually in Norway) for all levels, see snowsportengland.org.
This company provide week cross-country ski skills and race preparation courses (in addition to guided cross-country ski holidays). Further details: www.exodus.co.uk/
On Snow Skiing
There are many opportunities to cross-country ski on-snow abroad, search the internet and ask around for suggestions.
In addition to companies that specialise in cross-country resort holidays the main alpine ski companies go to a number of cross-country resorts often providing easier access with direct flights than possible with a self-arranged holiday.
Occasionally in Scotland there are cut tracks in Glenmoe Forest and Clashindarroch Forest near Huntly. In addition, both the Lecht and Glencoe ski centres have run Cross Country skiing events, including the occasional race.
Further details: https://www.britishnordic.org/where-to-ski
For those considering entering biathlon races it is advisable to have entered a number of cross-country races first. They will provide much of the biathlon experience, e.g pre-race preparation, skiing at race pace and skiing in a crowd, without the additional issues of carrying and operating a rifle under race conditions.
It is worth noting that cross-country races are normally substantially longer than biathlon races so you may want to select a shorter race (or only race hard for the first 10km or so).
There are rollerski races in the UK as well as public races and Masters race on-snow abroad.