These treatments are not generally available in the UK.

Intravenous immunoglobulin (IVIg) for the treatment of birdshot retinochoroidopathy. Authors: LeHoang P.; Cassoux N.; George F.; Kullmann N.; Kazatchkine M.D. 2000.
This paper describes the use of IVIg treatment for Birdshot. Of the eighteen patients treated and followed for 39 months, the results showed that most patients had an improvement in visual acuity (up to two lines) or vision remained stable. Macular oedema was improved in half of the cases.

Human Immunoglobulins in Intraocular Inflammation. ZÉRA TELLIER. France. 2007.
The author states that case studies and open trials have shown favourable results when IVIg has been used to treat Birdshot. The author also states that cortisteroids and immunosuppressives work in around a half of patients with their effectiveness limited by their iatrogenicity ( treatment causes another medical condition eg. prolonged high dose steroid causing diabetes).